Transient electronic devices comprising inorganic or hybrid inorganic and organic substrates and encapsulates

ABSTRACT

The invention provides transient devices, including active and passive devices that physically, chemically and/or electrically transform upon application of at least one internal and/or external stimulus. Incorporation of degradable device components, degradable substrates and/or degradable encapsulating materials each having a programmable, controllable and/or selectable degradation rate provides a means of transforming the device. In some embodiments, for example, transient devices of the invention combine degradable high performance single crystalline inorganic materials with selectively removable substrates and/or encapsulants.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 61/811,603, filed Apr. 12, 2013, U.S. ProvisionalPatent Application No. 61/828,935, filed May 30, 2013, and U.S.Provisional Patent Application No. 61/829,028, filed May 30, 2013, eachof which is hereby incorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made, at least in part, with United Statesgovernmental support awarded by the National Science Foundation awardno. 1242240 and the Defense Advanced Research Projects Agency award no.W911 NF-11-1-0254. The United States Government has certain rights inthis invention.

BACKGROUND OF INVENTION

This invention is in the field of transient devices, and relatesgenerally to passive and active devices designed to programmablytransform.

Transient devices have potential for a range of important applications.For example, eco-degradable environmental sensors avoid the need fordevice collection and bioresorbable medical devices that degrade and arecleared from the body avoid toxicity and inflammation. Strategically,military devices that degrade after a preselected time or uponapplication of a triggered stimulus avoid transferring knowledge ormaterials to enemies. All of these envisioned applications areimportant, but implementation of transient devices is dependent upondesign strategies. Design strategies for transient devices must (i)support device fabrication using degradable device component materialsand degradable substrates, (ii) provide for accurate control of theuseful lifetime of the device, and (iii) utilize materials that arecompatible with and perform adequately for a given application within atarget environment.

Recently, a number of patents and publications have disclosed deviceswith transient properties. For example, Kim et al., “Silicon electronicson silk as a path to bioresorbable implantable devices”, Appl. Phys.Lett. 95, 133701 (2009); U.S. Patent Application Publication2011/0230747; and International Patent Application Publication WO2008/085904 disclose biodegradable electronic devices that may include abiodegradable semiconducting material and a biodegradable substrate.Bettinger et al., “Organic thin film transistors fabricated onresorbable biomaterial substrates”, Adv. Mater., 22(5), 651-655 (2010);Bettinger et al., “Biomaterial-based organic electronic devices”, Poly.Int. 59(5), 563-576 (2010); and Irimai-Vladu, “Environmentallysustainable organic field effect transistors”, Organic Electronics, 11,1974-1990 (2010) disclose biodegradable electronic devices that mayinclude a biodegradable organic conducting material and a biodegradablesubstrate. International Patent Application Publication WO 2008/108838discloses biodegradable devices for delivering fluids and/or biologicalmaterial to tissue. U.S. Patent Application Publication 2008/0306359discloses ingestible devices for diagnostic and therapeuticapplications. Kozicki et al., “Programmable metallization cell memorybased on Ag—Ge—S and Cu—Ge—S solid electrolytes”, NonVolatile MemoryTechnology Symposium, 83-89 (2005) discloses memory devices where metalions within an electrolyte may be reduced or oxidized to form or removesolid metal interconnects.

SUMMARY OF THE INVENTION

The invention provides transient devices, including active and passivedevices that physically, chemically and/or electrically transform uponapplication of at least one internal and/or external stimulus.Incorporation of degradable device components, degradable substratesand/or degradable encapsulating materials each having a programmable,controllable and/or selectable degradation rate provide a means oftransforming the device. In some embodiments, for example, transientdevices of the invention combine degradable high performance singlecrystalline inorganic materials with selectively removable substratesand/or encapsulants.

This description presents a set of materials, modeling tools,manufacturing approaches, device designs and system level examples oftransient electronics. The present invention is directed to transientelectronic devices incorporating inorganic materials, for example, forstructure device components including substrates and encapsulants.Incorporation of inorganic materials in some transient devices of theinvention provides a means of engineering overall device properties toachieve a range of performance benefits. In some embodiments, forexample, inorganic device materials provide structural components, suchas substrates and encapsulant layers, capable of precisely defined andpreselected transience properties, such as transience profiles havingwell-defined temporal and physical properties useful for a range ofapplications. In some embodiments, for example, inorganic devicematerials provide structural components, such as substrates andencapsulant layers, that are effective electronic insulating and/orbarrier layers prior to a pre-engineered transient devicetransformation. In some embodiments, for example, inorganic devicematerials provide structural components, such as substrates andencapsulant layers, that undergo small dimensional changes prior to apre-engineered transient device transformation, for example, in responseto environmental conditions, e.g., exposure to water, biological fluidor other solvent, or in response to a user initiated trigger signal. Insome embodiments, for example, inorganic device materials of theinvention are compatible with processing approaches and materialsstrategies capable of achieving precisely controlled physical andchemical properties supporting a range of device applications.

In an embodiment, for example, the invention provides a transientelectronic device comprising: (i) a substrate; (ii) one or more activeor passive electronic device components supported by said substrate;wherein said active or passive electronic device componentsindependently comprise a selectively transformable material; and (iii)an encapsulant layer at least partially encapsulating said one or moreactive or passive electronic device components; wherein said substrate,said encapsulant layer or both independently comprise a selectivelyremovable inorganic material responsive to an external or internalstimulus; wherein at least partial removal of said substrate, saidencapsulant layer or both in response to said external or internalstimulus initiates at least partial transformation of said one or moreactive or passive electronic device components providing a programmabletransformation of the transient electronic device in response to saidexternal or internal stimulus at a pre-selected time or at apre-selected rate, wherein said programmable transformation provides achange in function of the transient electronic device from a firstcondition to a second condition. In an embodiment, for example, said oneor more active or passive electronic device components comprise one ormore inorganic semiconductor components, one or more metallic conductorcomponents or one or more inorganic semiconductor components and one ormore metallic conductor components.

The invention of this aspect includes transient devices wherein thesubstrate or encapsulant layer comprising a selectively removableinorganic material is completely removed during device transformation oronly partially removed (e.g., at least 20%, 30%, 50%, 70% or 90% byweight, volume or area removed) during device transformation. Transientelectronic devices of this aspect include passive transient devices andactively triggered transient devices.

In an embodiment, for example, the substrate, the encapsulant layer orboth independently comprises an entirely inorganic structure. Forexample, an entirely inorganic structure may include one or more ofSiO₂, spin-on-glass, Mg, Mg alloys, Fe, W, Zn, Mo, Si, SiGe, Si₃N₄ andMgO. Alternatively, the invention includes transient devices wherein thesubstrate, the encapsulant layer or both independently comprises acomposite inorganic and organic structure, for example, having amultilayer geometry combining one or more layers of an inorganicmaterial and one or more layers of an organic material, such as apolymer material. For example, a composite inorganic and organicstructure may comprise an inorganic layer having a first surfaceadjacent the active or passive electronic device components and a secondsurface adjacent an organic layer or a composite inorganic and organicstructure may comprise an organic layer having a first surface adjacentthe active or passive electronic device components and a second surfaceadjacent the inorganic layer. In an embodiment, the inorganic layercomprises one or more of SiO₂, spin-on-glass, Mg, Mg alloys, Fe, W, Zn,Mo, Si, SiGe, Si₃N₄ and MgO and the organic layer comprises one or moreof a polyanhydride and poly(dimethyl siloxane) (PDMS).

In an embodiment, transient devices of the invention include entirelyinorganic devices comprising all inorganic device components, forexample, wherein said active or passive electronic device components,said substrate and said encapsulant layer each are independentlyentirely composed of one or more inorganic materials. Transient devicesof the invention include hybrid inorganic-organic devices comprising acombination of one or more inorganic device components comprisingmetals, ceramics, metal oxides or glasses, and one or more organicdevice components, for example, comprising a polymer material.

In an embodiment, for example, the substrate, the encapsulant layer orboth independently has a preselected transience profile in response toan external or internal stimulus. A range of processing approaches andmaterials strategies are useful in the present invention for achievingan inorganic substrate and/or encapsulant layer having a preselectedtransience profile including selection of chemical composition, physicalproperties, morphology and control of synthesis, growth and/ordeposition processes.

Selection of the composition of substrates and encapsulant layerscomprising a selectively removable inorganic material is an importantaspect for achieving transience properties useful for supporting a rangeof device functionalities. In an embodiment, the composition of thesubstrate and/or encapsulant layer is selected to achieve usefulelectronic, physical and/or transience properties. In an embodiment, forexample, the selectively removable inorganic material of the substrate,the encapsulant layer or both independently comprises a metal, a metaloxide, a ceramic or a combination of these. In an embodiment, forexample, the selectively removable inorganic material of the substrateor the encapsulant layer independently comprises a crystalline material,an amorphous material or a combination thereof. In an embodiment, forexample, the selectively removable inorganic material of the substrate,the encapsulant layer or both independently comprises a singlecrystalline material, polycrystalline material or doped crystallinematerial. In an embodiment, for example, the selectively removableinorganic material of the substrate, the encapsulant layer or bothindependently comprises a glass, such as a spin-on-glass.

In an embodiment, for example, the selectively removable inorganicmaterial of the substrate, the encapsulant layer or both independentlycomprises a thin film, a coating, a foil or any combination of these. Inan embodiment, for example, the selectively removable inorganic materialof the substrate, the encapsulant layer or both independently comprisesa nanofilm having a thickness ranging from 1 nm to 100 nm or a microfilmhaving a thickness ranging from 1 μm to 100 μm. In an embodiment, forexample, the substrate, the encapsulant layer or both independentlycomprises a nanostructured layer or a microstructured layer, for examplea layer having one or more perforations, cavities and/or channelsprovided on an external or internal surface of the substrate orencapsulant layer or provided within the substrate or encapsulant layer.In an embodiment, an encapsulation layer entirely encapsulates at leasta portion, and optionally all, of the underlying active or passiveelectronic device components, such as underlying semiconductorcomponents and/or metallic conductor components. In an embodiment, anencapsulation layer encapsulates only a portion of the underlying activeor passive electronic device components, such as underlyingsemiconductor components and/or metallic conductor components (e.g., 90%or less, 70% or less, 30% or less, etc.).

In an embodiment, for example, the selectively removable inorganicmaterial of the substrate, the encapsulant layer or both independentlycomprises Mg, W, Mo, Fe, Zn, or an alloy thereof. In an embodiment, forexample, the selectively removable inorganic material of the substrate,the encapsulant layer or both independently comprises SiO₂, MgO, N₄Si₃,SiC or any combination of these. In an embodiment, for example, theselectively removable inorganic material of the substrate, theencapsulant layer or both independently comprises a spin-on-glass orsolution processable glass. In an embodiment, for example, theselectively removable inorganic material of the substrate, theencapsulant layer or both independently comprises a biocompatiblematerial, a bioinert material or a combination of biocompatible andbioinert materials.

Substrate and encapsulation layers of the present transient electronicdevices include multilayer structures, for example, multilayerstructures comprising one or more inorganic device component layers andone or more organic device component layers. In an embodiment, forexample, a multilayer substrate and encapsulation layers comprise aninorganic layer having a first side in contact (e.g., physical contactor electrical contact) with an organic layer. In an embodiment, forexample, a multilayer substrate and encapsulation layers comprise aninorganic layer provided between, and optionally in physical contactwith, a plurality of organic layers. Use of multilayer substrate andencapsulation layers having both organic and inorganic layers allows forcomponents having precisely selectable chemical, physical and electronicproperties, for example, resistance, inertness, permeability to water,resistance to swelling, chemical stability, optical transmission, etc.In an embodiment, for example, a multilayer substrate or encapsulationlayer comprises 2 to 100 layers, and optionally for some applications 5to 20 layers.

In an embodiment, for example, the substrate, the encapsulant layer orboth independently comprises a multilayer structure comprising one ormore of a thin film, coating, or foil comprising the selectivelyremovable inorganic material. In an embodiment, for example, themultilayer structure comprises a stack of layers including the one ormore thin films, coatings, or foils comprising the selectively removableinorganic material and further including one or more additional layers,such as layers comprising an organic material, such as a polymer layer,or an insulating ceramic material, such as SiO₂. Incorporation oforganic layers (e.g. polymer layers) or an insulating ceramic material,such as SiO₂, into multilayer substrates and encapsulating layers of theinvention is beneficial for providing electrical insulation between aconductive component (e.g., metal) of the substrate or encapsulant layerand underlying device components. In addition, incorporation of organiclayers (e.g. polymer layers) or an insulating ceramic material, such asSiO₂, into multilayer substrates and encapsulating layers of theinvention is beneficial for providing a useful overall permeability ofthe substrate or encapsulating layer, for example, to prevent volumechanges via swelling. In an embodiment, for example, a multilayersubstrate or encapsulation layer comprises 2 to 100 inorganic layers and2 to 100 organic layers, optionally where at least a portion of theorganic layers are disposed between inorganic layers.

In an embodiment, for example, the multilayer structure of the presentsubstrate or encapsulant layer further comprises one or moreelectrically insulating layers, barrier layers or any combinationsthereof. In some embodiments, a barrier layer of the invention adjuststhe permeability of a device component, for example, by decreasing theoverall permeability of the component to water, solvent or environmentalfluid. In an embodiment, for example, one or more electricallyinsulating layers or barrier layers are provided in physical contact,electrical contact or both with the one or more thin films, coatings, orfoils. In an embodiment, for example, the one or more electricallyinsulating layers or barrier layers comprises an exterior layer of themultilayer structure. In an embodiment, for example, the one or moreelectrically insulating layers or barrier layers comprises an interiorlayer of the multilayer structure in physical contact or electricalcontact with the one or more active or passive electronic devicecomponents, such as one or more inorganic semiconductor components, oneor more metallic conductor components or both. In an embodiment, forexample, the one or more electrically insulating layers or barrierlayers comprises a polymer, an insulating ceramic, a glass, SiO₂,spin-on-glass, MgO or any combination of these.

In an embodiment, for example, the multilayer structure of the presentsubstrate and/or encapsulant layer comprises a metal foil or thin metalfilm having a first side in physical contact with a first electronicallyinsulating layer or barrier layer. In an embodiment, for example, thefirst electronically insulating layer or barrier layer is an exteriorlayer of the multilayer structure or the first electronically insulatinglayer or barrier layer is an interior layer of the multilayer structurein physical contact or electrical contact with the one or more active orpassive electronic device components, such as one or more inorganicsemiconductor components, one or more metallic conductor components orboth. In an embodiment, for example, the first electronically insulatinglayer or barrier layer comprises a polymer or insulating ceramic layeror coating, a metal oxide layer or coating, a glass layer or coating orany combination of these. In an embodiment, for example, the multilayerstructure comprises the metal foil or thin metal film having a secondside coated in contact with a second electronically insulating layer orbarrier layer; wherein the metal foil or thin metal film is providedbetween the first electronically insulating layer or barrier layer andthe second electronically insulating layer or barrier layer.

Substrates and encapsulants of certain embodiments comprise selectivelyremoval materials exhibiting a transience profile useful for aparticular device application. In an embodiment, for example, at leastpartial removal of the substrate, the encapsulant layer or both exposesthe one or more active or passive electronic device components, such asone or more inorganic semiconductor components or one or more metallicconductor components, to the external or internal stimulus, therebyinitiating the at least partial transformation of the one or more activeor passive electronic device components, such as one or more inorganicsemiconductor components or the one or more metallic conductorcomponents. In an embodiment, for example, at least partial removal ofthe substrate, the encapsulant layer or both in response to the internalor external stimulus occurs via a phase change, dissolution, hydrolysis,bioresorption, etching, corrosion, a photochemical reaction, anelectrochemical reaction or any combination of these processes.

In an embodiment, at least partial removal of the substrate, encapsulantlayer or both occurs by a process other than bioresorption. In anotherembodiment, at least partial removal of the substrate, encapsulant layeror both occurs via at least partial dissolution of the selectivelyremovable inorganic material in a solvent. The solvent may be an aqueoussolvent or a nonaqueous solvent. An “aqueous solvent” is a liquid at 298K that predominantly comprises water, i.e., greater than 50% v/v water,whereas a “nonaqueous solvent” is a liquid at 298 K that predominantlycomprises liquid(s) other than water, i.e., less than 50% v/v water.Exemplary aqueous solvents include water, water-based solutions, bodilyfluids, and the like. Exemplary nonaqueous solvents include organicsolvents (e.g., alcohols, esters, ethers, alkanes, ketones) and ionicliquids. In another embodiment, at least partial removal of thesubstrate, encapsulant layer or both occurs via at least partialhydrolysis of the selectively removable inorganic material. In anotherembodiment, at least partial removal of the substrate, encapsulant layeror both occurs via at least partial etching or corrosion of theselectively removable inorganic material. In another embodiment, atleast partial removal of the substrate, encapsulant layer or both occursby a photochemical reaction wherein at least a portion of theselectively removable inorganic material absorbs electromagneticradiation, and undergoes an at least partial chemical or physicalchange. In an embodiment, the photochemical reaction is aphotodecomposition process. In another embodiment, at least partialremoval of the substrate, encapsulant layer or both occurs by anelectrochemical reaction. For example, the electrochemical reaction maybe at least partial anodic dissolution of the selectively removableinorganic material of the substrate, encapsulant layer or both.

In an embodiment, for example, the substrate, the encapsulant layer orboth independently have a preselected transience profile characterizedby a removal of 0.01% to 100% by weight of the substrate or theencapsulant layer over a time interval selected from the range of 1 msto 5 years, or 1 ms to 2 years, or 1 ms to 1 year, or 1 ms to 6 months,or 1 ms to 1 month, or 1 ms to 1 day, or 1 ms to 1 hour, or 1 second to10 minutes. In an embodiment, for example, the substrate, theencapsulant layer or both independently have a preselected transienceprofile characterized by a decrease in average thickness of thesubstrate or the encapsulant layer at a rate selected over the range of0.01 nm/day to 100 microns s⁻¹, or 0.01 nm/day to 10 microns s⁻¹, or 0.1nm/day to 1 micron s⁻¹, or 1 nm/day to 0.5 micron s⁻¹. In an embodiment,for example, the substrate or the encapsulant layer or bothindependently has a porosity selected from the range of 0.01% to 99.9%prior to the at least partial removal of the substrate, the encapsulantlayer or both in response to the external or internal stimulus.

The physical properties of substrates and encapsulation layerscomprising a selectively removable inorganic material may be selected toachieve desired transience properties. In an embodiment, for example,the substrate, the encapsulant layer or both independently has an extentof crystallinity selected from the range of 0.1% to 100%, or 0.1% to99.9%, or 1% to 90%, or 5% to 80%, or 10% to 60%, or 15% to 40% prior tothe at least partial removal of the substrate, the encapsulant layer orboth in response to the external or internal stimulus. In an embodiment,for example, the encapsulant layer or both independently has a densityselected from the range of 0.1% to 100%, or 0.1% to 99.9%, or 1% to 90%,or 5% to 80%, or 10% to 60%, or 15% to 40% compared to bulk prior to theat least partial removal of the substrate, the encapsulant layer or bothin response to the external or internal stimulus. In an embodiment, forexample, a time for a thickness of the selectively removable material toreach zero is provided by the expression:

${t_{c} = {\frac{4\rho_{m}{M\left( {H_{2}O} \right)}}{{kw}_{0}{M(m)}}\frac{\sqrt{\frac{{kh}_{0}^{2}}{D}}}{\tanh \sqrt{\frac{{kh}_{0}^{2}}{D}}}}};$

(EX1); where t_(c) is the critical time, ρ_(m) is the mass density ofthe material, M(H₂O) is the molar mass of water, M(m) is the molar massof the material, h_(o) is the initial thickness of the material, D isthe diffusivity of water, k is the reaction constant for the dissolutionreaction, and w₀ is the initial concentration of water; wherein k has avalue selected from the range of 1×10⁵ s⁻¹ to 1×10⁻¹⁰ s⁻¹.

Substrates and encapsulant layers comprising a selectively removableinorganic material may have a range of physical, electronic and chemicalproperties useful for a particular application. In an embodiment, forexample, the substrate, the encapsulant layer or both are substantiallyimpermeable to water prior to the at least partial removal of thesubstrate, the encapsulant layer or both in response to the external orinternal stimulus. In an embodiment, for example, the substrate, theencapsulant layer or both limit a net leakage current to thesurroundings to 0.1 μA/cm² or less prior to the at least partial removalof the substrate, the encapsulant layer or both in response to theexternal or internal stimulus. In an embodiment, for example, thesubstrate, the encapsulant layer or both undergo an increase in volumeequal to or less than 10%, or equal to or less than 5%, or equal to orless than 3%, or equal to or less than 1% upon exposure to an aqueous ornonaqueous solvent prior to the at least partial removal of thesubstrate, the encapsulant layer or both in response to the external orinternal stimulus. In an embodiment, for example, a thin film, coating,or foil of the substrate or encapsulant layer has an average thicknessover or underneath of the one or more active or passive electronicdevice components, such as one or more inorganic semiconductorcomponents or one or more metallic conductor components, less than orequal to 1000 μm, or less than or equal to 500 μm, or less than or equalto 250 μm, or less than or equal to 100 μm, or less than or equal to 50μm prior to the at least partial removal of the substrate, theencapsulant layer or both in response to the external or internalstimulus. In an embodiment, for example, the substrate, the encapsulantlayer or both independently has a thickness selected from the range of0.1 μm to 1000 μm, or of 1 μm to 500 μm, or of 5 μm to 100 μm, or of 10μm to 50 μm prior to the at least partial removal of the substrate, theencapsulant layer or both in response to the external or internalstimulus. In an embodiment, for example, the substrate, the encapsulantlayer or both independently has an average modulus selected over therange of 0.5 KPa to 10 TPa, or of 5 KPa to 1 TPa, or of 50 KPa to 1 TPa,or of 5 GPa to 500 GPa. In an embodiment, for example, the substrate,the encapsulant layer or both independently has a net flexural rigidityless than or equal to 1×10⁻⁴ Nm. In an embodiment, for example, thesubstrate, the encapsulant layer or both independently has a net bendingstiffness less than or equal to 1×10⁸ GPa μm⁴, or less than or equal to1×10⁶ GPa μm⁴, or less than or equal to 1×10⁵ GPa μm⁴, or less than orequal to 1×10³ GPa μm⁴. In an embodiment, for example, the substrate,the encapsulant layer or both are at least partially opticallytransparent in the visible or infrared regions of the electromagneticspectrum.

Useful substrates and encapsulating layers comprising a selectivelyremovable inorganic material may be fabricated via a range of processingapproaches, including deposition techniques, solution processing andspin casting. In an embodiment, for example, the substrate, theencapsulant layer or both is generated via physical vapor deposition,chemical vapor deposition, sputtering, atomic layer deposition,electrochemical deposition, spin casting, electrohydrodynamic jetprinting, screen printing or any combination of these. In an embodiment,for example, the substrate, the encapsulant layer or both covers orsupports a percentage of an exterior area or volume or an interior areaor volume of the one or more active or passive electronic devicecomponents, such as one or more inorganic semiconductor components, oneor more metallic conductor components or both, selected from the rangeof 1% to 100%, optionally selected over the range of 10 to 50%. In anembodiment, for example, the substrate, the encapsulant layer or bothcovers or supports 10% or more, optionally 30% or more, of an exteriorarea or an interior area of the one or more inorganic semiconductorcomponents, one or more metallic conductor components or both.

In an embodiment, the one or more active or passive electronic devicecomponents comprise one or more one or more inorganic semiconductorcomponents. In an embodiment, for example, the one or more inorganicsemiconductor components comprise a polycrystalline semiconductormaterial, a single crystalline semiconductor material or a dopedpolycrystalline or single crystalline semiconductor material. In anembodiment, for example, the one or more inorganic semiconductorcomponents comprise Si, Ga, GaAs, ZnO or any combination of these. In anembodiment, the one or more active or passive electronic devicecomponents comprise one or more one or more metallic conductorcomponents. In an embodiment, for example, the one or more metallicconductor components comprise Mg, W, Mo, Fe, Zn or an alloy thereof. Inan embodiment, for example, the one or more active or passive electronicdevice components comprise a component of an electronic device selectedfrom the group consisting of a transistor, a diode, an amplifier, amultiplexer, a light emitting diode, a laser, a photodiode, anintegrated circuit, a sensor, a temperature sensor, an electrochemicalcell, a thermistor, a heater, a resistive heater, an antenna, ananoelectromechanical system or a microelectromechanical system, anactuator and arrays thereof.

In an embodiment, for example, the device is a communication system, aphotonic device, a sensor, an optoelectronic device, a biomedicaldevice, a temperature sensor, a photodetector, a photovoltaic device, astrain gauge, and imaging system, a wireless transmitter, anelectrochemical cell, an antenna, a nanoelectromechanical system, anenergy storage system, an actuator or a microelectromechanical system.

In an embodiment, a transient electronic device has a preselectedtransience profile characterized by the transformation of the one ormore active or passive electronic device components, such as one or moreinorganic semiconductor components or the one or more metallic conductorcomponents, occurring over a time interval selected from the range of 1ms to 2 years, or 1 ms to 1 year, or 1 ms to 6 months, or 1 ms to 1month, or 1 ms to 1 day, or 1 ms to 1 hour, or 1 second to 10 minutes,thereby providing the programmable transformation of the passivetransient electronic device. In an embodiment, the preselectedtransience profile is characterized by a transformation of 0.01% to100%, or 0.1% to 70%, or 0.5% to 50%, or 1% to 20% or 1% to 10% of theone or more active or passive electronic device components, such as oneor more inorganic semiconductor components or the one or more metallicconductor components, over a time interval selected from the range of 1ms to 2 years, or 1 ms to 1 year, or 1 ms to 6 months, or 1 ms to 1month, or 1 ms to 1 day, or 1 ms to 1 hour, or 1 second to 10 minutes,thereby providing the programmable transformation of the passivetransient electronic device. In an embodiment, the preselectedtransience profile is characterized by a decrease in the averagethickness of the one or more active or passive electronic devicecomponents, such as one or more inorganic semiconductor components orthe one or more metallic conductor components, at a rate selected overthe range of 0.01 nm/day to 10 microns s⁻¹, or 0.1 nm/day to 1 microns⁻¹, or 1 nm/day to 0.5 micron s⁻¹. In an embodiment, the preselectedtransience profile is characterized by a decrease in the mass of the oneor more active or passive electronic device components, such as one ormore inorganic semiconductor components or the one or more metallicconductor components, at a rate selected over the range of 0.01 nm/dayto 10 microns s⁻¹, or 0.1 nm/day to 1 micron s⁻¹, or 1 nm/day to 0.5micron s⁻¹. In an embodiment, the preselected transience profile ischaracterized by a decrease in the electrical conductivity of the one ormore active or passive electronic device components, such as one or moreinorganic semiconductor components or the one or more metallic conductorcomponents, at a rate selected over the range of 10¹⁰ S·m⁻¹ s⁻¹ to 1S·m⁻¹ s⁻¹, or 10⁸ S·m⁻¹ s⁻¹ to 10 S·m⁻¹ s⁻¹, or 10⁵ S·m⁻¹ s⁻¹ to 100S·m⁻¹ s⁻¹.

The physical dimensions and shape of the device, and components thereof,are important parameters, particularly with respect to preselection of adesired transience profile. Use of thin electronic device components,such as inorganic semiconductor components, metallic conductorcomponents and/or dielectric components (e.g., thickness less than orequal to 100 microns, optionally thickness less than or equal to 10microns, optionally thickness less than or equal to 1 micron, optionallythickness less than or equal to 500 nanometers, and optionally thicknessless than or equal to 100 nanometers) is beneficial for providing apreselected transience for a given device application and/or providinguseful mechanical properties such as a flexible or otherwise deformabledevice. In some embodiments, inorganic semiconductor components,metallic conductor components and/or dielectric components independentlycomprise one or more thin film structures, which may for example bedeposited or grown by molecular epitaxy, atomic layer deposition,physical or chemical vapor deposition, or other methods known in theart. In some embodiments, one or more inorganic semiconductorcomponents, metallic conductor components and/or dielectric componentsindependently comprise a biocompatible, bioresorbable, bioinert orecocompatible material. In some embodiments, at least some of, andoptionally all of, the inorganic semiconductor components, metallicconductor components and/or dielectric components of the electronicdevice have a thickness less than or equal to 100 microns, and for someapplications have a thickness less than or equal to 10 microns, and forsome applications have a thickness less than or equal to 1 micron, andfor some applications have a thickness less than or equal to 500nanometers, and for some applications have a thickness less than orequal to 100 nanometers, and for some applications have a thickness lessthan or equal to 20 nanometers. In some embodiments, at least some of,and optionally all of, the inorganic semiconductor components, metallicconductor components and/or dielectric components of the deviceindependently have a thickness selected from a range of 10 nm to 100 μm,optionally for some applications selected from a range of 50 nm to 10μm, and optionally for some applications selected from a range of 100 nmto 1000 nm. In an embodiment, for example, a device of the inventioncomprises one or more inorganic semiconductor components eachindependently having a thickness selected over the range of 10 nm to1000 nm, optionally for some applications 10 nm to 100 nm and optionallyfor some applications 10 nm to 30 nm. In some embodiments, at least someof, and optionally all of, the inorganic semiconductor components,metallic conductor components and/or dielectric components of the deviceindependently have lateral physical dimensions (e.g., length, width,diameter, etc.) less than or equal to 10000 μm, and for someapplications have lateral physical dimensions less than or equal to 1000μm, and for some applications have lateral physical dimensions less thanor equal to 100 μm, and for some applications have lateral physicaldimensions less than or equal to 1 μm. In some embodiments, at leastsome of, and optionally all of, the inorganic semiconductor components,metallic conductor components and/or dielectric components of the deviceindependently have lateral physical dimensions selected from the rangeof 10 nm to 10 cm, optionally for some applications selected from arange of 100 nm to 10000 μm, optionally for some applications selectedfrom a range of 500 nm to 1000 μm, optionally for some applicationsselected from a range of 500 nm to 100 μm, and optionally for someapplications selected from a range of 500 nm to 10 μm.

The physical properties of the semiconductor components, metallicconductor components and/or selectively removable inorganic materialcomponents (e.g., Young's modulus, net bending stiffness, toughness,conductivity, resistance, etc.) impact the performance and transience ofthe device. In some embodiments, for example, at least a portion, andoptionally all, of the semiconductor components, metallic conductorcomponents and/or selectively removable inorganic material components ofthe device independently have a Young's modulus less than or equal to 10GPa, optionally for some applications less than or equal to 100 MPa,optionally for some applications less than or equal to 10 MPa. In someembodiments, for example, at least a portion, and optionally all, of thesemiconductor components, metallic conductor components and/orselectively removable inorganic material components of the device have aYoung's modulus selected over the range of 0.5 MPa and 10 GPa, andoptionally for some applications selected over the range of 0.5 MPa and100 MPa, and optionally for some applications selected over the range of0.5 MPa and 10 MPa. In some embodiments, at least a portion, andoptionally all, of the semiconductor components, metallic conductorcomponents and/or selectively removable inorganic material components ofthe device have a net bending stiffness less than or equal to 1×10⁸ GPaμm⁴, optionally for some applications less than or equal to 5×10⁵ GPaμm⁴ and optionally for some applications less than or equal to 1×10⁵ GPaμm⁴. In some embodiments, at least a portion, and optionally all, of thesemiconductor components, metallic conductor components and/orselectively removable inorganic material components of the device have anet bending stiffness selected over the range of 0.1×10⁴ GPa μm⁴ and1×10⁸ GPa μm⁴, and optionally for some applications between 0.1×10 GPaμm⁴ and 5×10⁵ GPa μm⁴.

Useful materials for the inorganic semiconductor components include highquality semiconductor materials such as single crystalline semiconductormaterials including pure and doped single crystalline semiconductormaterials. In an embodiment, all of the inorganic semiconductorcomponents comprise a single crystalline semiconductor material and/or asingle crystalline doped semiconductor material, for example, singlecrystalline silicon and/or doped single crystalline silicon derived fromhigh temperature foundry processing. Integration of single crystallinesemiconductor materials into a transient device is particularlybeneficial for providing devices exhibiting very good electronicproperties. In an embodiment, the semiconductor components comprise amaterial selected from the group consisting of Si, Ge, Se, diamond,fullerenes, SiC, SiGe, SiO, SiO₂, SiN, AlSb, AlAs, AlIn, AlN, AlP, AlS,BN, BP, BAs, As₂S₃, GaSb, GaAs, GaN, GaP, GaSe, InSb, InAs, InN, InP,CsSe, CdS, CdSe, CdTe, Cd₃P₂, Cd₃As₂, Cd₃Sb₂, ZnO, ZnSe, ZnS, ZnTe,Zn₃P₂, Zn₃As₂, Zn₃Sb₂, ZnSiP₂, CuCl, PbS, PbSe, PbTe, FeO, FeS₂, NiO,EuO, EuS, PtSi, TIBr, CrBr₃, SnS, SnTe, PbI₂, MoS₂, GaSe, CuO, Cu₂O,HgS, HgSe, HgTe, HgI₂, MgS, MgSe, MgTe, CaS, CaSe, SrS, SrTe, BaS, BaSe,BaTe, SnO₂, TiO, TiO₂, Bi₂S₃, Bi₂O₃, Bi₂Te₃, BiI_(a), UO₂, UO₃, AgGaS₂,PbMnTe, BaTiO₃, SrTiO₃, LiNbO₃, La₂CuO₄, La_(0.7)Ca_(0.3)MnO₃, CdZnTe,CdMnTe, CuInSe₂, copper indium gallium selenide (CIGS), HgCdTe, HgZnTe,HgZnSe, PbSnTe, TI₂SnTe₅, TI₂GeTe₅, AlGaAs, AlGaN, AlGaP, AlInAs,AlInSb, AlInP, AlInAsP, AlGaAsN, GaAsP, GaAsN, GaMnAs, GaAsSbN, GaInAs,GaInP, AlGaAsSb, AlGaAsP, AlGaInP, GaInAsP, InGaAs, InGaP, InGaN,InAsSb, InGaSb, InMnAs, InGaAsP, InGaAsN, InAlAsN, GaInNAsSb, GaInAsSbP,and any combination of these. In some embodiments, the inorganicsemiconductor components include a material selected from the groupconsisting of Si, SiC, SiGe, SiO, SiO₂, SiN, and any combination ofthese. In some embodiments, the inorganic semiconductor componentsindependently comprise single crystalline silicon, porous silicon and/orpolycrystalline silicon. In some embodiments, the inorganicsemiconductor components independently comprise a polycrystallinesemiconductor material, single crystalline semiconductor material ordoped polycrystalline or single crystalline semiconductor material. Insome embodiments, the inorganic semiconductor component is atransformable material. Useful materials for a transformable, inorganicsemiconductor component include, but are not limited to, porous silicon,polycrystalline silicon, and any combination of these.

In some embodiments, electronic devices comprise one or moreinterconnected island and bridge structures. For example, an islandstructure may comprise one or more semiconductor circuit components ofthe transient device. A bridge structure may comprise one or moreflexible and/or stretchable electrical interconnections providingelectrical communication between elements, for example between differentisland structures. In this manner, electronic devices of the presentinvention may comprise stretchable electronic devices having a pluralityof electrically interconnected inorganic semiconductor componentscomprising one or more island structures and one or more flexible and/orstretchable bridge structures providing electrical interconnection;e.g., stretchable electronic interconnects.

In some embodiments, the transient device, or components thereof, areassembled on the substrate via a printing-based or molding-basedprocess, for example, by transfer printing, dry contact transferprinting, solution-based printing, soft lithography printing, replicamolding, imprint lithography, etc. In some of these embodiments,therefore, the device, or components thereof, comprise printablesemiconductor materials and/or devices. Integration of the device andsubstrate components via a printing-based technique is beneficial insome embodiments, as it allows for independent processing ofsemiconductor devices/materials and processing for the substrate. Forexample, the printing-based assembly approach allows semiconductordevices/materials to be processed via techniques that would not becompatible with some substrates. In some embodiments, for example, thesemiconductor devices/materials are first processed via high temperatureprocessing, physical and chemical deposition processing, etching and/oraqueous processing (e.g. developing, etc.), and then subsequentlyassembled on the substrate via a printing-based technique. An advantageof this approach is that it avoids processing of the semiconductordevices/materials on the substrate in a manner that could negativelyimpact the chemical and/or physical properties of the substrate, forexample, by negatively impacting biocompatibility, toxicity and/or thedegradation properties (e.g., degradation rate, etc.) of thetransformable substrate. In some embodiments, for example, this approachallows for effective fabrication of the device without exposing thesubstrate to aqueous processing, for example, processing involvingexposure of the transformable substrate to an etchant, a stripper or adeveloper.

In some embodiments, the transient device may include one or moreadditional device components selected from the group consisting of anelectrode, a dielectric layer, a chemical or biological sensor element,a pH sensor, an optical sensor, an optical source, a temperature sensor,and a capacitive sensor. The additional device component may comprise abioinert material, a degradable material or a transformable material.Useful bioinert materials include, but are not limited to, titanium,gold, silver, platinum and any combination of these. Useful degradableor transformable materials include, but are not limited to, iron,magnesium, tungsten and any combination of these.

In an aspect, the invention provides a method of using a transientelectronic device, the method comprising the steps of: (i) providing thetransient electronic device comprising: (1) a substrate; (2) one or moreactive or passive electronic device components supported by saidsubstrate; wherein said active or passive electronic device componentsindependently comprise a selectively transformable material; and (3) anencapsulant layer at least partially encapsulating said one or moreactive or passive electronic device components; wherein said substrate,said encapsulant layer or both independently comprise a selectivelyremovable inorganic material responsive to an external or internalstimulus; wherein at least partial removal of said substrate, saidencapsulant layer or both in response to said external or internalstimulus initiates at least partial transformation of said one or moreactive or passive electronic device components providing a programmabletransformation of the transient electronic device in response to saidexternal or internal stimulus at a pre-selected time or at apre-selected rate, wherein said programmable transformation provides achange in function of the transient electronic device from a firstcondition to a second condition; and (ii) exposing said transientelectronic device to said external or internal stimulus resulting insaid at least partial removal of said substrate or encapsulant layer toexpose said one or more active or passive electronic device componentsto said external or internal stimulus, thereby providing saidprogrammable transformation of the transient electronic device. In anembodiment of this aspect, for example, said one or more active orpassive electronic device components comprise one or more inorganicsemiconductor components, one or more metallic conductor components orone or more inorganic semiconductor components and one or more metallicconductor components.

In an embodiment, for example, the invention provides a method whereinsaid removal of said substrate, said encapsulant layer or both inresponse to said internal or external stimulus occurs via a phasechange, dissolution, hydrolysis, bioresorption, etching, corrosion, aphotochemical reaction, an electrochemical reaction or any combinationof these processes. In an embodiment, for example, the inventionprovides a method wherein said step of exposing said transientelectronic device to said external or internal stimulus results in theentire removal of said substrate, said encapsulant layer or both. In anembodiment, for example, the invention provides a method wherein saidstep of exposing said transient electronic device to said external orinternal stimulus results in less than the entire removal of saidsubstrate, said encapsulant layer or both. In an embodiment, forexample, the invention provides a method wherein said step of exposingsaid transient electronic device to said external or internal stimulusexposes at least 1% of an outer surface of said one or more active orpassive electronic device components, optionally for some applicationsat least 10% of an outer surface of said one or more active or passiveelectronic device components, and optionally for some applications atleast 50% of an outer surface of said one or more active or passiveelectronic device components. In an embodiment, for example, theinvention provides a method wherein said step of exposing said transientelectronic device to said external or internal stimulus exposes 1% to100% of an outer surface of said one or more active or passiveelectronic device components, optionally for some applications 10% to100% of an outer surface of said one or more active or passiveelectronic device components, optionally for some applications 50% to100% of an outer surface of said one or more active or passiveelectronic device components

In an aspect, the invention provides a method of making a transientelectronic device, said method comprising the steps of: (i) providing asubstrate; (ii) providing on said substrate one or more active orpassive electronic device components; wherein said active or passiveelectronic device components independently comprise a selectivelytransformable material; and (iii) at least partially encapsulating saidone or more active or passive electronic device components with anencapsulant layer; wherein said substrate, said encapsulant layer orboth independently comprise a selectively removable inorganic materialresponsive to an external or internal stimulus; wherein at least partialremoval of said substrate, said encapsulant layer or both in response tosaid external or internal stimulus initiates at least partialtransformation of said one or more active or passive electronic devicecomponents providing a programmable transformation of the transientelectronic device in response to said external or internal stimulus at apre-selected time or at a pre-selected rate, wherein said programmabletransformation provides a change in function of the transient electronicdevice from a first condition to a second condition.

Without wishing to be bound by any particular theory, there may bediscussion herein of beliefs or understandings of underlying principlesrelating to the devices and methods disclosed herein. It is recognizedthat regardless of the ultimate correctness of any mechanisticexplanation or hypothesis, an embodiment of the invention cannonetheless be operative and useful.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. FIGS. 1A-1D provide schematic diagrams illustrating side viewsof transient electronic devices of the invention.

FIG. 2. Time dependent change in the thicknesses of thin layers of PECVDSiO₂ in PBS at room temperature and 37° C.

FIG. 3. Time dependent change in the thicknesses of thin layers ofthermally grown SiO₂ (wet and dry oxidation) at different pH in PBSsolutions at room temperature, and 37° C.

FIG. 4. Change in resistance of test structures of various metals in (a)DI water and (b) pH 7.4 Hank's solution.

FIG. 5. The schematic illustration of inorganic layered substratestructure, using metal foils coated with spin-on-glass (SOG).

FIG. 6. Dissolution kinetics of SiO₂ in aqueous solution at different pHand temperature (1) SiO₂ thermally grown by dry or wet oxidation, (2)SiO₂ deposited by plasma enhanced chemical vapor deposition and (3) SiO₂deposited by electron beam evaporation. Calculated (lines) andexperimental (symbols) dissolution rates of silicon oxides in buffersolution at different pH (black, pH 7.4; red, pH 8; blue, pH 10;magenta, pH 12) at room (left) and physiological (right, 37° C.)temperature. The thickness was measured by spectroscopic ellipsometry.

FIG. 7. (A) Measured data (symbols) and numerical fits (lines) forpH-dependent dissolution kinetics of oxides (black, tg-oxide by dryoxidation; red, tg-oxide by wet oxidation; blue, PECVD oxide; magenta,E-beam oxide) at room temperature and 37° C. (B) SiO₂ film propertydependency exhibited as film density versus dissolution rate.

FIG. 8. Experimental results for dissolution study of SiN_(x). The plotsprovide measurements of thickness (nm) as a function of time (days).

FIG. 9. (A) pH-dependent dissolution kinetics of nitrides (black, LPCVDnitride; red, PECVD nitride with LF mode; blue, PE-CVD nitride with HFmode) at room temperature and 37° C. (B) SiN_(x) film propertydependency exhibited as film density versus dissolution rate.

FIG. 10. Dissolution kinetics for different oxides immersed in variousaqueous solutions. A) Bovine serum (pH ˜7.4) at 37° C. (black, tg-oxideby dry oxidation; red, tg-oxide by wet oxidation; blue, PECVD oxide;magenta, E-beam oxide), B) sea water (pH ˜7.8) at RT (black, tg-oxide bydry oxidation; red, tg-oxide by wet oxidation; blue, PECVD oxide;magenta, E-beam oxide), C) Bovine serum (pH ˜7.4) at 37° C. (black,LPCVD nitride; red, PECVD nitride with LF mode; blue, PECVD nitride withHF mode), D) sea water (pH ˜7.8) at RT (black, LPCVD nitride; red, PECVDnitride with LF mode; blue, PECVD nitride with HF mode).

FIG. 11. Curing mechanism and dissolution study of spin-on-glassencapsulation layers cured at various temperatures and times.

FIG. 12. pH dependent dissolution studies of amorphous silicon (a-Si),polycrystalline silicon (p-Si) and silicon germanide (SiGe).

FIG. 13. Electrical dissolution rates and thicknesses of sputterdeposited Mg, Mg alloy (AZ31B, Al 3%, Zn 1%), Zn, Mo, W, CVD depositedW, and E-beam evaporated Fe in DI water and Hanks' solution with pH 5-8.

FIG. 14. Current versus voltage plots for devices containing transientmetal components.

FIG. 15. Photographs showing dissolution of a transient transistor arrayon a biodegradable metal foil.

FIG. 16. Dissolution kinetics of various metal foils (Mo, Zn, Fe, W)under physiological conditions (PBS, pH 7.4, 37° C.).

FIG. 17. Schematic of a fabrication strategy using metal foils. 1)Lamination of metal foil on a carrier substrate (e.g., PDMS coated onglass), 2) fabrication of a transistor array directly on the metal foil,and 3) peeling of the device from the carrier substrate.

FIG. 18. Demonstrations of inorganic substrates.

FIG. 19. Schematic illustrations of encapsulation methods for transientelectronic devices, showing defects (e.g. pinholes) covered by a bilayerof SiO₂/Si₃N₄; ALD provides a defect-free layer.

FIG. 20. (A) Measurements of changes in resistance of Mg traces (˜300 nmthick) encapsulated with different materials and thicknesses whileimmersed in deionized (DI) water at room temperature. A single layer ofALD SiO₂ (orange, 20 nm), PECVD SiO₂ (black, 1 μm) and PECVD-LF Si₃N₄(red, 1 μm), a double layer of PECVD SiO₂/PECVD-LF Si₃N₄ (blue, 500/500nm), PECVD SiO₂/ALD SiO₂ (magenta, 500/20 nm), PECVD-LF Si₃N₄/ALD SiO₂(purple, 500/20 nm), and a triple layer of PECVD SiO₂/PECVD-LF Si₃N₄(Cyan, 200/200/200/200/100/100 nm) were used for the encapsulation.

FIG. 21. A series of micrographs of a serpentine trace of Mg (initially˜300 nm thick) during dissolution in DI water at room temperature.Dissolution begins from local defects, then rapidly propagates outward.

FIG. 22. Demonstration of the electrical properties of electronicdevices fabricated on metal foils. (A) Transistor array on Fe foil (˜10μm thick), (B) Diode array on Zn foil (˜10 μm thick), (C) Capacitorarray on Mo foil (˜10 μm thick), (D) Inductor array on Mo foil (˜10 μmthick).

FIG. 23. Transience of transient devices on inorganic substrates withinorganic encapsulation. (A) Transistor on Mo foil with MgOencapsulation (˜800 nm), (B) Diode on Mo foil with MgO encapsulation(˜800 nm), (C) Capacitor on Mo foil with MgO encapsulation (˜800 nm),(D) Inductor on Mo foil with MgO encapsulation.

FIG. 24. Sample structure for a dissolution test of single wafer SiGe(Ge) with atomic force microscopy (AFM). (a) Schematic illustration oftest structure: array of square holes (3 μm×3 μm×20 nm) of PECVD SiO₂mask on SiGe single wafer. (b) AFM topographical images and c) profilesof SiGe, at different stages of dissolution in buffer solution (pH 10)at 37° C.

FIG. 25. Dissolution kinetics of various semi-conductors in variousbuffer solutions, with different pH at room and physiologicaltemperatures. (a) polycrystalline silicon, (b) amorphous silicon, (c)silicon-germanium and (d) germanium.

FIG. 26. Dissolution kinetics of different types of silicon in variousaqueous solutions. (a) Tap water (pH ˜7.8), deionized water (DI, pH˜8.1) and spring water (pH ˜7.4), (b) Coke (pH ˜2.6), (c) milk (pH ˜6.4)at room temperature, (d) bovine serum (pH ˜7.4) at room and 37° C., and(e) sea water (pH ˜7.8) at room temperature. (f) Changes in resistanceof a meander trace formed from a phosphorous doped polycrystalline andamorphous Si NM (˜35 nm) in phosphate buffer solution (pH 10) at 37° C.

FIG. 27. Thin film solar cell with fully transient materials. (a), (b)Image and structure of amorphous Si based photovoltaic cell array ondegradable substrate. (c) Performance of unit cell of solar cells. (d)Electrical transience behavior of a-Si diode and (e) transience ofperformance of solar cell.

FIG. 28. Schematic illustration, images and data from a structure fortesting the dissolution of thin (˜100 nm thick) square pads of SiO₂formed by plasma-enhanced chemical vapor deposition (PECVD). a)Schematic illustration of the test structure, which consists of an arrayof square pads (3 μm×3 μm×100 nm) of PECVD SiO₂ deposited at 350° C. ona thermally grown oxide (tg-oxide) on a silicon (100) wafer, with insetoptical micrograph. b) AFM topographical images and c) profiles of arepresentative pad at different stages of hydrolysis in buffer solution(pH 12) at physiological temperature (37° C.).

FIG. 29. AFM surface topography and thickness profile for PECVD oxide atvarious stages of dissolution in (a), (b) buffer solution (pH 7.4) at37° C., and (c), (d) buffer solution (pH 10) at 37° C.

FIG. 30. AFM surface topography and thickness profile for E-beam oxideat various stages of dissolution in buffer solution with (a), (b) pH7.4, and (c), (d) pH 8, and (e), (f) pH 10, at 37° C.

FIG. 31. Dissolution kinetics, as defined by the rate of change of filmthicknesses, of different silicon oxides in various aqueous solutions,with different values of pH at room and physiological temperature's. a)Calculated (lines) and measured (symbols) values for the time-dependentdissolution of thermally grown SiO₂ (dry oxidation) in buffer solutions(black, pH 7.4; red, pH 8; blue, pH 10; purple, pH 12) at room (left)and physiological (right, 37° C.) temperature. b) Calculated (lines) andmeasured (symbols) dissolution behaviors of PECVD SiO₂ in diverseaqueous solutions with different pH at room (left) and physiological(right, 37° C.) temperature. c) Calculated (lines) and experimental(symbols) results of dissolution studies on E-beam SiO₂ in aqueoussolutions at different pH and temperature. d) Dependence of dissolutionkinetics of silicon oxide films on pH (black, tg-oxide (dry); red,tg-oxide (wet); blue, PECVD SiO₂; purple, E-beam SiO₂) at physiologicaltemperature (37° C.) corresponding to experimental data (symbol) andnumerical fits (line). e) Measurements of dissolution rates of siliconoxides as a function of film density in buffer solution (pH 7.4) at room(black) and physiological (red, 37° C.) temperature.

FIG. 32. Bonding energy of Si 2p for tg-oxide (black, dry oxidation),PECVD oxide (red), and E-beam oxide (blue) measured by XPS.

FIG. 33. Measured density of several oxides (black, tg-oxide by dryoxidation; red, tg-oxide by wet oxidation; blue, PECVD oxide; magenta,E-beam oxide) determined by XRR. The triangles indicate the criticalangles.

FIG. 34. TEM images and diffraction patterns (inset) of a) PECVD oxideand b) E-beam oxide.

FIG. 35. AFM measurements of surface roughness of PECVD SiO₂ whileimmersed in different pH solutions at 37° C. a) Average surfaceroughness (Ra) at various stages of dissolution in buffer solution(black, pH 7.4; red, pH 8; blue, pH 10; magenta, pH 12), b) surfacetopographic images after 6 days in buffer solution (top right, pH 7.4;bottom left, pH 10; bottom right, pH 12).

FIG. 36. Dissolution kinetics via hydrolysis of various silicon nitridesin aqueous solutions at different pH and temperature. a) Calculated(lines) and measured (symbols) values for the dissolution of Si₃N₄formed by low-pressure chemical-vapor deposition (LPCVD) in buffersolutions (black, pH 7.4; red, pH 8; blue, pH 10; purple, pH 12) at room(left) and physiological (right, 37° C.) temperature. b) Calculated(lines) and measured (symbols) dissolution behaviors of PECVD Si₃N₄(low-frequency mode) in diverse aqueous solutions with different pH atroom (left) and physiological (right, 37° C.) temperature. c) Calculated(lines) and experimental (symbols) results of dissolution study on PECVDSi₃N₄ (high-frequency mode) in aqueous solutions at different pH andtemperature. d) Calculated (lines) and experimental (symbols) results ofthe dependence of dissolution kinetics of silicon nitride films on pH(black, LP-CVD Si₃N₄; red, PE-CVD Si₃N₄ (low frequency); blue, PE-CVDSi₃N₄ (high frequency)) at physiological temperature (37° C.). e)Measured dissolution rate of silicon nitrides as a function of filmdensity in buffer solution (pH 7.4) at room (black) and physiological(red, 37° C.) temperature.

FIG. 37. Densities of nitrides (black, LPCVD nitride; red, PECVD nitridewith LF mode; blue, PECVD nitride with HF mode) measured by XRR. Thetriangles indicate the critical angles.

FIG. 38. Measurements of changes in thickness of ALD SiO₂ duringimmersion in buffer solution (pH 7.4) at 37° C.

FIG. 39. (A) Structures of the components of mixture 7A of Table 3showing reactive groups. (B) Component ratios and indication thatdegradation rate increases as hydrophobicity decreases. (C) Reactionscheme for forming a polyanhydride encapsulant material comprising aphosphodiester group within the polymeric chain. (D) Reaction scheme forforming a polyanhydride encapsulant material comprising a silyl ethergroup within the polymeric chain. (E) Reaction scheme for forming apolyanhydride encapsulant material comprising an ether group within thepolymeric chain.

FIG. 40. Schematic of water permeability test set-up.

FIG. 41. Performance of the organic encapsulants compared to materialsof other classes, such as inorganic encapsulants, as change in conductorresistance over time.

FIG. 42. Dissolution rates of three polyanhydrides (A: A1T1, B: A1T2, C:A1T4) in buffer solutions with pH 5.7 (squares), pH 7.4 (circles) and pH8 (triangles).

DETAILED DESCRIPTION OF THE INVENTION

In general, the terms and phrases used herein have their art-recognizedmeaning, which can be found by reference to standard texts, journalreferences and contexts known to those skilled in the art. The followingdefinitions are provided to clarify their specific use in the context ofthe invention.

“Functional layer” refers to a layer that imparts some functionality tothe device. For example, the functional layer may contain semiconductorcomponents, metallic components, dielectric components, opticalcomponents, piezoelectric components, etc. Alternatively, the functionallayer may comprise multiple layers, such as multiple semiconductorlayers, metallic layers or dielectric layers separated by supportlayers. The functional layer may comprise a plurality of patternedelements, such as interconnects running between electrodes or islands.The functional layer may be heterogeneous or may have one or moreproperties that are inhomogeneous. “Inhomogeneous property” refers to aphysical parameter that can spatially vary, thereby effecting theposition of the neutral mechanical plane within a multilayer device.

“Structural layer” refers to a layer that imparts structuralfunctionality, for example by supporting, securing and/or encapsulatingdevice components. The invention includes transient devices having oneor more structural layers, such as encapsulating layers, embeddinglayers, adhesive layers and/or substrate layers.

“Semiconductor” refers to any material that is an insulator at a verylow temperature, but which has an appreciable electrical conductivity ata temperature of about 300 Kelvin. In the present description, use ofthe term semiconductor is intended to be consistent with use of thisterm in the art of microelectronics and electronic devices. Usefulsemiconductors include those comprising elemental semiconductors, suchas silicon, germanium and diamond, and compound semiconductors, such asgroup IV compound semiconductors such as SiC and SiGe, group III-Vsemiconductors such as AlSb, AlAs, AlN, AlP, BN, BP, BAs, GaSb, GaAs,GaN, GaP, InSb, InAs, InN, and InP, group III-V ternary semiconductorsalloys such as Al_(x)Ga_(1-x)As, group II-VI semiconductors such asCsSe, CdS, CdTe, ZnO, ZnSe, ZnS, and ZnTe, group I-VII semiconductorssuch as CuCl, group IV-VI semiconductors such as PbS, PbTe, and SnS,layer semiconductors such as PbI₂, MoS₂, and GaSe, oxide semiconductorssuch as CuO and Cu₂O. The term semiconductor includes intrinsicsemiconductors and extrinsic semiconductors that are doped with one ormore selected materials, including semiconductors having p-type dopingmaterials and n-type doping materials, to provide beneficial electronicproperties useful for a given application or device. The termsemiconductor includes composite materials comprising a mixture ofsemiconductors and/or dopants. Specific semiconductor materials usefulfor some embodiments include, but are not limited to, Si, Ge, Se,diamond, fullerenes, SiC, SiGe, SiO, SiO₂, SiN, AlSb, AlAs, AlIn, AlN,AlP, AlS, BN, BP, BAs, As₂S₃, GaSb, GaAs, GaN, GaP, GaSe, InSb, InAs,InN, InP, CsSe, CdS, CdSe, CdTe, Cd₃P₂, Cd₃As₂, Cd₃Sb₂, ZnO, ZnSe, ZnS,ZnTe, Zn₃P₂, Zn₃As₂, Zn₃Sb₂, ZnSiP₂, CuCl, PbS, PbSe, PbTe, FeO, FeS₂,NiO, EuO, EuS, PtSi, TIBr, CrBr₃, SnS, SnTe, PbI₂, MoS₂, GaSe, CuO,Cu₂O, HgS, HgSe, HgTe, HgI₂, MgS, MgSe, MgTe, CaS, CaSe, SrS, SrTe, BaS,BaSe, BaTe, SnO₂, TiO, TiO₂, Bi₂S₃, Bi₂O₃, Bi₂Te₃, BiI₃, UO₂, UO₃,AgGaS₂, PbMnTe, BaTiO₃, SrTiO₃, LiNbO₃, La₂CuO₄, La_(0.7)Ca_(0.3)MnO₃,CdZnTe, CdMnTe, CuInSe₂, copper indium gallium selenide (CIGS), HgCdTe,HgZnTe, HgZnSe, PbSnTe, TI₂SnTe₅, TI₂GeTe₅, AlGaAs, AlGaN, AlGaP,AlInAs, AlInSb, AlInP, AlInAsP, AlGaAsN, GaAsP, GaAsN, GaMnAs, GaAsSbN,GaInAs, GalnP, AlGaAsSb, AlGaAsP, AlGaInP, GaInAsP, InGaAs, InGaP,InGaN, InAsSb, InGaSb, InMnAs, InGaAsP, InGaAsN, InAlAsN, GaInNAsSb,GaInAsSbP, and any combination of these. Porous silicon semiconductormaterials are useful for aspects described herein. Impurities ofsemiconductor materials are atoms, elements, ions and/or molecules otherthan the semiconductor material(s) themselves or any dopants provided tothe semiconductor material. Impurities are undesirable materials presentin semiconductor materials which may negatively impact the electronicproperties of semiconductor materials, and include but are not limitedto oxygen, carbon, and metals including heavy metals. Heavy metalimpurities include, but are not limited to, the group of elementsbetween copper and lead on the periodic table, calcium, sodium, and allions, compounds and/or complexes thereof.

A “semiconductor component” broadly refers to any semiconductormaterial, composition or structure, and expressly includes high qualitysingle crystalline and polycrystalline semiconductors, semiconductormaterials fabricated via high temperature processing, dopedsemiconductor materials, inorganic semiconductors, and compositesemiconductor materials.

A “component” is used broadly to refer to an individual part of adevice. An “interconnect” is one example of a component, and refers toan electrically conducting structure capable of establishing anelectrical connection with another component or between components. Inparticular, an interconnect may establish electrical contact betweencomponents that are separate. Depending on the desired devicespecifications, operation, and application, an interconnect is made froma suitable material. Suitable conductive materials includesemiconductors and metallic conductors.

Other components include, but are not limited to, thin film transistors(TFTs), transistors, diodes, electrodes, integrated circuits, circuitelements, control elements, photovoltaic elements, photovoltaic elements(e.g. solar cell), sensors, light emitting elements, actuators,piezoelectric elements, receivers, transmitters, microprocessors,transducers, islands, bridges and combinations thereof. Components maybe connected to one or more contact pads as known in the art, such as bymetal evaporation, wire bonding, and application of solids or conductivepastes, for example. Electronic devices of the invention may compriseone or more components, optionally provided in an interconnectedconfiguration.

“Neutral mechanical plane” (NMP) refers to an imaginary plane existingin the lateral, b, and longitudinal, l, directions of a device. The NMPis less susceptible to bending stress than other planes of the devicethat lie at more extreme positions along the vertical, h, axis of thedevice and/or within more bendable layers of the device. Thus, theposition of the NMP is determined by both the thickness of the deviceand the materials forming the layer(s) of the device. In an embodiment,a device of the invention includes one or more inorganic semiconductorcomponents, one or more metallic conductor components or one or moreinorganic semiconductor components and one or more metallic conductorcomponents provided coincident with, or proximate to, the neutralmechanical plane of the device.

“Coincident” refers to the relative position of two or more objects,planes or surfaces, for example a surface such as a neutral mechanicalplane that is positioned within or adjacent to a layer, such as afunctional layer, substrate layer, or other layer. In an embodiment, aneutral mechanical plane is positioned to correspond to the moststrain-sensitive layer or material within the layer.

“Proximate” refers to the relative position of two or more objects,planes or surfaces, for example a neutral mechanical plane that closelyfollows the position of a layer, such as a functional layer, substratelayer, or other layer while still providing desired conformabilitywithout an adverse impact on the strain-sensitive material physicalproperties. “Strain-sensitive” refers to a material that fractures or isotherwise impaired in response to a relatively low level of strain. Ingeneral, a layer having a high strain sensitivity, and consequentlybeing prone to being the first layer to fracture, is located in thefunctional layer, such as a functional layer containing a relativelybrittle semiconductor or other strain-sensitive device element. Aneutral mechanical plane that is proximate to a layer need not beconstrained within that layer, but may be positioned proximate orsufficiently near to provide a functional benefit of reducing the strainon the strain-sensitive device element when the device is conformed to atissue surface. In some embodiments, proximate to refers to a positionof a first element within 100 microns of a second element, or optionallywithin 10 microns for some embodiments, or optionally within 1 micronfor some embodiments.

“Electronic device” generally refers to a device incorporating aplurality of components, and includes large area electronics, printedwire boards, integrated circuits, component arrays, biological and/orchemical sensors, physical sensors (e.g., temperature, strain, etc.),nanoelectromechanical systems, microelectromechanical systems,photovoltaic devices, communication systems, medical devices, opticaldevices, energy storage systems, actuators and electro-optic devices.

“Sensing” refers to detecting the presence, absence, amount, magnitudeor intensity of a physical and/or chemical property. Useful electronicdevice components for sensing include, but are not limited to electrodeelements, chemical or biological sensor elements, pH sensors,temperature sensors, strain sensors, mechanical sensors, positionsensors, optical sensors and capacitive sensors.

“Actuating” refers to stimulating, controlling, or otherwise affecting astructure, material or device component, such as one or more inorganicsemiconductor components, one or more metallic conductor components oran encapsulating material or layer. In an embodiment, actuating refersto a process in which a structure or material is selectivelytransformed, for example, so as to undergo a chemical or physical changesuch as removal, loss or displacement of a material or structure. Usefulelectronic device components for actuating include, but are not limitedto, electrode elements, electromagnetic radiation emitting elements,light emitting diodes, lasers, magnetic elements, acoustic elements,piezoelectric elements, chemical elements, biological elements, andheating elements.

An “actuator” is a device component that directly or indirectlyinitiates at least partial transformation of a transient electronicdevice in response to a user initiated external trigger signal, forexample by initiating an at least partial transformation of aselectively transformable material of a transient electronic device. Forexample, an actuator may initiate at least partial transformation of atransient device by absorbing energy supplied to the device andutilizing or converting that energy to affect the at least partialtransformation. For example, an actuator may initiate at least partialtransformation of a transient device by exposing a device componentcomprising selectively transformable material to an internal or externalstimulus resulting in an at least partial transformation. For example,an actuator may initiate at least partial transformation of a transientdevice by supplying energy (e.g., thermal, electromagnetic radiation,acoustic, RF energy, etc.) to an intermediate material or devicecomponent which affects the transformation, such as supplying energy toan encapsulating material, inorganic semiconductor components, ormetallic conductor components. Thus, the actuator may comprise a singlecomponent or multiple components that alone or in combination facilitatetransformation of the transient electronic device. In some embodiments,an actuator of the invention is directly or indirectly provided incommunication with a transmitter, for example, via one or more receiverdevice components.

A “user initiated trigger signal” includes any action, other than themere placement of a transient device in a particular environment, bywhich a person may start or initiate a programmable transformation of atransient device. Exemplary “user initiated trigger signals” includeproviding real-time user input data to the device or a transmitter incommunication with the device (e.g., pressing a button, flipping aswitch, setting a timer, etc.), providing at least one non-ambientexternal source of energy directly or indirectly to the device (e.g., anelectric field, a magnetic field, acoustic energy, pressure, strain,heat, light, mechanical energy, etc.), and/or programming software toexecute computer-readable instructions, which may be based on datareceived from the device, for example data from a feedback loop. In anembodiment, the user initiated external trigger signal is an electronicsignal, an optical signal, a thermal signal, a magnetic signal, amechanical signal, a chemical signal, an acoustic signal or anelectrochemical signal. In an embodiment, the invention provides atransient electronic device configured to receive a user initiatedtrigger signal, for example, a user initiated trigger signal provided bya transmitter and received by a receiver component of the device.

A “non-ambient external source of energy” includes energy having amagnitude at least 10% greater, or at least 25% greater, or at least 50%greater than the magnitude of ubiquitous energy of the same form foundin the environment in which a transient device is located.

The terms “directly and indirectly” describe the actions or physicalpositions of one component relative to another component. For example, acomponent that “directly” acts upon or touches another component does sowithout intervention from an intermediary. Contrarily, a component that“indirectly” acts upon or touches another component does so through anintermediary (e.g., a third component).

“Island” refers to a relatively rigid component of an electronic devicecomprising a plurality of semiconductor components. “Bridge” refers tostructures interconnecting two or more islands or one island to anothercomponent. Specific bridge structures include semiconductor and metallicinterconnects. In an embodiment, a transient device of the inventioncomprises one or more semiconductor-containing island structures, suchas transistors, electrical circuits or integrated circuits, electricallyconnected via one or more bridge structures comprising electricalinterconnects.

“Encapsulate” refers to the orientation of one structure such that it isat least partially, and in some cases completely, surrounded by one ormore other structures, such as a substrate, adhesive layer orencapsulating layer. “Partially encapsulated” refers to the orientationof one structure such that it is partially surrounded by one or moreother structures, for example, wherein 30%, or optionally 50%, oroptionally 90%, of the external surface of the structure is surroundedby one or more structures. “Completely encapsulated” refers to theorientation of one structure such that it is completely surrounded byone or more other structures. The invention includes transient deviceshaving partially or completely encapsulated inorganic semiconductorcomponents, metallic conductor components and/or dielectric components,for example, via incorporation of a polymer encapsulant, such as abiopolymer, silk, a silk composite, or an elastomer encapsulant.

“Barrier layer” refers to a component spatially separating two or moreother components or spatially separating a component from a structure,material, fluid or environment external to the device. In oneembodiment, a barrier layer encapsulates one or more components. In someembodiments, a barrier layer separates one or more components from anaqueous solution, a biological tissue or both. The invention includesdevices having one or more barrier layers, for example, one or morebarrier layers positioned at the interface of the device with anexternal environment.

A barrier layer(s), and optionally a sacrificial layer on a substrate,may be etched to produce a “mesh structure”, where at least a portion ofthe barrier layer(s), and optionally the sacrificial layer on asubstrate, is removed. For example a portion of the barrier layer(s)disposed approximately 10 nanometers or more from an inorganicsemiconductor component or additional component is removed. Removal ofat least a portion of the barrier layer(s), and optionally thesacrificial layer on the substrate, may produce (i) one or more holeswithin the barrier layer(s) and/or (ii) electrical components, which arephysically joined by a barrier layer(s) at a proximal end and physicallyseparated at a distal end. In one embodiment, a mesh structure may bedisposed upon a contiguous substrate, which provides structural supportfor the device during deployment into an environment.

“Contiguous” refers to materials or layers that are touching orconnected throughout in an unbroken sequence. In one embodiment, acontiguous layer of an implantable biomedical device has not been etchedto remove a substantial portion (e.g., 10% or more) of the originallyprovided material or layer.

“Active circuit” and “active circuitry” refer to one or more componentsconfigured for performing a specific function. Useful active circuitsinclude, but are not limited to, amplifier circuits, multiplexingcircuits, current limiting circuits, integrated circuits, transistorsand transistor arrays. The present invention includes devices whereinthe one or more inorganic semiconductor components, one or more metallicconductor components and/or one or more dielectric components comprisean active circuit or plurality of active circuits.

“Substrate” refers to a material, layer or other structure having asurface, such as a receiving surface, that is capable of supporting oneor more components or devices. A component that is “bonded” to thesubstrate refers to a component that is in physical contact with thesubstrate and unable to substantially move relative to the substratesurface to which it is bonded. Unbonded components or portions of acomponent, in contrast, are capable of substantial movement relative tothe substrate. In an embodiment, the invention provides devices whereinone or more inorganic semiconductor components, one or more metallicconductor components and/or one or more dielectric components aredirectly or indirectly bonded to the substrate, for example, via anadhesive layer or via an adhesion layer.

A “selectively transformable material” is a material that undergoes aphysical change and/or a chemical change under pre-selected and/orpredetermined conditions, such as conditions of time, pressure,temperature, chemical or biological composition, and/or electromagneticradiation. Selectively transformable materials useful for some deviceapplications undergo a physical transformation, such as a phase changeincluding melting, sublimation, etc., optionally at a preselected timeor at a preselected rate or in response to a preselected set ofconditions or change in conditions. Selectively transformable materialsuseful for some device applications undergo a chemical transformation,such as decomposition, disintegration, dissolution, hydrolysis,resorption, bioresporption, photodecomposition, depolymerization,etching, or corrosion, optionally at a preselected time or at apreselected rate or in response to a preselected set of conditions orchange in conditions. The pre-selected condition(s) may occur naturally,for example, provided by conditions of a device environment (e.g.,ambient temperature, pressure, chemical or biological environment,natural electromagnetic radiation, etc.) or may occur via artificialcondition(s) provided to, or within, a transient electronic device, suchas a user or device initiated temperature, pressure, chemical orbiological environment, electromagnetic radiation, magnetic conditions,mechanical strain, or electronic conditions. When the selectivelytransformable material of a transient electronic device is exposed tothe condition(s) that initiate transformation of the material, theselectively transformable material may be substantially completely orcompletely transformed at a “pre-selected time” or a “pre-selectedrate”. Devices of the invention include selectively transformablematerials that undergo a complete transformation, substantially completetransformation or an incomplete transformation. A selectivelytransformable material that is “substantially completely” transformed is95% transformed, or 98% transformed, or 99% transformed, or 99.9%transformed, or 99.99% transformed, but not completely (i.e., 100%)transformed. In some embodiments, a selectively transformable materialundergoes a chemical change resulting in a change in a physical,chemical, electronic or optoelectronic property, optionally at apre-selected time or at a pre-selected rate. In an embodiment, forexample, a selectively transformable material undergoes a chemical orphysical change resulting in a change of a first compositioncharacterized by a conducting or semiconducting material to a secondcomposition characterized as an insulator. In some embodiments, aselectively transformable material is a selectively removable material.

A “selectively removable material” is a material that is physicallyand/or chemically removed under pre-selected or predetermined conditionssuch as conditions of time, pressure, temperature, chemical orbiological composition, and/or electromagnetic radiation. In anembodiment, for example, a selectively removable material is removed viaa process selected from the group consisting of decomposition,disintegration, dissolution, hydrolysis, resorption, bioresporption,photodecomposition, and depolymerization, optionally at a preselectedtime or at a preselected rate or in response to a preselected set ofconditions or change in conditions. In an embodiment, for example, aselectively removable material is removed by undergoing a phase change,such as melting or sublimation, resulting in loss or relocation of thematerial, optionally at a preselected time or at a preselected rate orin response to a preselected set of conditions or change in conditions.The pre-selected condition(s) may occur naturally, for example, providedby conditions of a device environment (e.g., ambient temperature,pressure, chemical or biological environment, natural electromagneticradiation, etc.) or may occur via artificial condition(s) provided to,or within, a transient electronic device, such as a user or deviceinitiated temperature, pressure, chemical or biological environment,electromagnetic radiation, electronic conditions. When the selectivelyremovable material of a transient electronic device is exposed to thecondition(s) that initiate removal of the material, the selectivelyremovable material may be substantially completely removed, completelyremoved or incompletely removed at a “pre-selected time” or a“pre-selected rate”. A selectively removable material that is“substantially completely” removed is 95% removed, or 98% removed, or99% removed, or 99.9% removed, or 99.99% removed, but not completely(i.e., 100%) removed.

A “pre-selected time” refers to an elapsed time from an initial time,t₀. For example, a pre-selected time may refer to an elapsed time from acomponent/device fabrication or deployment, to a critical time, t_(c),for example, when the thickness of a selectively removable materialexposed to a pre-selected condition(s) reaches zero, or substantiallyzero (10% or less of initial thickness, 5% or less of initial thickness,1% or less of initial thickness) or when a property (e.g. conductance orresistivity) of a selectively removable material reaches a thresholdvalue; e.g., a decrease in conductivity equal to 50%, optionally forsome applications 80%, and optionally for some applications 95% oralternatively when conductivity equals 0. In an embodiment, thepreselected time may be calculated according to:

${t_{c} = {\frac{4\rho_{m}{M\left( {H_{2}O} \right)}}{{kw}_{0}{M(m)}}\frac{\sqrt{\frac{{kh}_{0}^{2}}{D}}}{\tanh \sqrt{\frac{{kh}_{0}^{2}}{D\;}}}}};$

where t_(c) is the critical time, ρ_(m) is the mass density of thematerial, M(H₂O) is the molar mass of water, M(m) is the molar mass ofthe material, h₀ is the initial thickness of the material, D is thediffusivity of water, k is the reaction constant for the dissolutionreaction, and w₀ is the initial concentration of water.

A “pre-selected rate” refers to an amount of selectively removablematerial removed from a device or component per unit time. Thepre-selected rate may be reported as an average rate (over the lifetimeof the device or component) or an instantaneous rate. When a rate typeis not specified, an average rate is assumed.

A “programmable transformation” refers to a pre-selected orpredetermined physical, chemical and/or electrical change within atransient electronic device that provides a change of the function ofthe device from a first condition to a second condition. A programmabletransformation may be pre-set at the time of component/devicefabrication or deployment or a real-time triggered programmabletransformation controlled by a transmitter that provides a signalreceived by the device.

A “transience profile” describes a change in physical parameters orproperties (e.g., thickness, conductivity, resistance, mass, porosity,etc.) of a material as a function of time, e.g., thickness gained/lostover time. A transience profile may be characterized by a rate, forexample, the rate of change of the physical dimensions (e.g., thickness)or physical properties (e.g., mass, conductivity, porosity, resistance,etc.) of a selectively transformable material. The invention includesselectively transformable materials having a transience profilecharacterized by a rate of change of the physical dimensions (e.g.,thickness) or physical properties (e.g., mass, conductivity, etc.) thatis constant or varies as a function of time.

“Degradable” refers to material that is susceptible to being chemicallyand/or physically broken down into smaller segments. Degradablematerials may, for example, be decomposed, resorbed, dissolved,absorbed, corroded, de-polymerized and/or disintegrated. In someembodiments, the invention provides degradable devices.

“Bioresorbable” refers to a material that is susceptible to beingchemically broken down into lower molecular weight chemical moieties byreagents that are naturally present in a biological environment. In anin-vivo application, the chemical moieties may be assimilated into humanor animal tissue. A bioresorbable material that is “substantiallycompletely” resorbed is highly resorbed (e.g., 95% resorbed, or 98%resorbed, or 99% resorbed, or 99.9% resorbed, or 99.99% resorbed), butnot completely (i.e., 100%) resorbed. In some embodiments, the inventionprovides bioresorbable devices.

“Biocompatible” refers to a material that does not elicit animmunological rejection or detrimental effect when it is disposed withinan in-vivo biological environment. For example, a biological markerindicative of an immune response changes less than 10%, or less than20%, or less than 25%, or less than 40%, or less than 50% from abaseline value when a biocompatible material is implanted into a humanor animal. In some embodiments, the invention provides biocompatibledevices.

“Bioinert” refers to a material that does not elicit an immune responsefrom a human or animal when it is disposed within an in-vivo biologicalenvironment. For example, a biological marker indicative of an immuneresponse remains substantially constant (plus or minus 5% of a baselinevalue) when a bioinert material is implanted into a human or animal. Insome embodiments, the invention provides bioinert devices.

“Ecocompatible” refers to a material that is environmentally benign inthat it may be degraded or decomposed into one or more compounds thatoccur naturally in the environment. In some embodiments, the inventionprovides ecocompatible devices.

“Nanostructured material” and “microstructured material” refer tomaterials having one or more nanometer-sized and micrometer-sized,respectively, physical dimensions (e.g., thickness) or features such asrecessed or relief features, such as one or more nanometer-sized andmicrometer-sized channels, voids, pores, pillars, etc. The relieffeatures or recessed features of a nanostructured material have at leastone physical dimension selected from the range of 1-1000 nm, while therelief features or recessed features of a microstructured material haveat least one physical dimension selected from the range of 1-1000 μm.Nanostructured and microstructured materials include, for example, thinfilms (e.g., microfilms and nanofilms), porous materials, patterns ofrecessed features, patterns of relief features, materials havingabrasive or rough surfaces, and the like. A nanofilm structure is alsoan example of a nanostructured material and a microfilm structure is anexample of a microstructured material. In an embodiment, the inventionprovides devices comprising one or more nanostructured ormicrostructured inorganic semiconductor components, one or morenanostructured or microstructured metallic conductor components, one ormore nanostructured or microstructured dielectric components, one ormore nanostructured or microstructured encapsulating layers and/or oneor more nanostructured or microstructured substrate layers.

A “nanomembrane” is a structure having a thickness selected from therange of 1-1000 nm or alternatively for some applications a thicknessselected from the range of 1-100 nm, for example provided in the form ofa ribbon, cylinder or platelet. In some embodiments, a nanoribbon is asemiconductor, dielectric or metallic conductor structure of anelectronic device. In some embodiments, a nanoribbon has a thicknessless than 1000 nm and optionally less than 100 nm. In some embodiments,a nanoribbon has a ratio of thickness to a lateral dimension (e.g.,length or width) selected from the range of 0.1 to 0.0001.

“Dielectric” refers to a non-conducting or insulating material. In anembodiment, an inorganic dielectric comprises a dielectric materialsubstantially free of carbon. Specific examples of inorganic dielectricmaterials include, but are not limited to, silicon nitride, silicondioxide, silk, silk composite, elastomers and polymers.

“Polymer” refers to a macromolecule composed of repeating structuralunits connected by covalent chemical bonds or the polymerization productof one or more monomers, often characterized by a high molecular weight.The term polymer includes homopolymers, or polymers consistingessentially of a single repeating monomer subunit. The term polymer alsoincludes copolymers, or polymers consisting essentially of two or moremonomer subunits, such as random, block, alternating, segmented,grafted, tapered and other copolymers. Useful polymers include organicpolymers or inorganic polymers that may be in amorphous, semi-amorphous,crystalline or partially crystalline states. Crosslinked polymers havinglinked monomer chains are particularly useful for some applications.Polymers useable in the methods, devices and components include, but arenot limited to, plastics, elastomers, thermoplastic elastomers,elastoplastics, thermoplastics and acrylates. Exemplary polymersinclude, but are not limited to, acetal polymers, biodegradablepolymers, cellulosic polymers, fluoropolymers, nylons, polyacrylonitrilepolymers, polyamide-imide polymers, polyimides, polyarylates,polybenzimidazole, polybutylene, polycarbonate, polyesters,polyetherimide, polyethylene, polyethylene copolymers and modifiedpolyethylenes, polyketones, poly(methyl methacrylate),polymethylpentene, polyphenylene oxides and polyphenylene sulfides,polyphthalamide, polypropylene, polyurethanes, styrenic resins,sulfone-based resins, vinyl-based resins, rubber (including naturalrubber, styrene-butadiene, polybutadiene, neoprene, ethylene-propylene,butyl, nitrile, silicones), acrylic, nylon, polycarbonate, polyester,polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyolefinor any combinations of these.

“Elastomeric stamp” and “elastomeric transfer device” are usedinterchangeably and refer to an elastomeric material having a surfacethat can receive as well as transfer a material. Exemplary conformaltransfer devices useful in some methods of the invention includeelastomeric transfer devices such as elastomeric stamps, molds andmasks. The transfer device affects and/or facilitates material transferfrom a donor material to a receiver material. In an embodiment, a methodof the invention uses a conformal transfer device, such as anelastomeric transfer device (e.g. elastomeric stamp) in a microtransferprinting process, for example, to transfer one or more singlecrystalline inorganic semiconductor structures, one or more dielectricstructures and/or one or more metallic conductor structures from afabrication substrate to a device substrate.

“Elastomer” refers to a polymeric material which can be stretched ordeformed and returned to its original shape without substantialpermanent deformation. Elastomers commonly undergo substantially elasticdeformations. Useful elastomers include those comprising polymers,copolymers, composite materials or mixtures of polymers and copolymers.Elastomeric layer refers to a layer comprising at least one elastomer.Elastomeric layers may also include dopants and other non-elastomericmaterials. Useful elastomers include, but are not limited to,thermoplastic elastomers, styrenic materials, olefinic materials,polyolefin, polyurethane thermoplastic elastomers, polyamides, syntheticrubbers, PDMS, polybutadiene, polyisobutylene,poly(styrene-butadiene-styrene), polyurethanes, polychloroprene andsilicones. In some embodiments, an elastomeric stamp comprises anelastomer. Exemplary elastomers include, but are not limited to siliconcontaining polymers such as polysiloxanes including poly(dimethylsiloxane) (i.e. PDMS and h-PDMS), poly(methyl siloxane), partiallyalkylated poly(methyl siloxane), poly(alkyl methyl siloxane) andpoly(phenyl methyl siloxane), silicon modified elastomers, thermoplasticelastomers, styrenic materials, olefinic materials, polyolefin,polyurethane thermoplastic elastomers, polyamides, synthetic rubbers,polyisobutylene, poly(styrene-butadiene-styrene), polyurethanes,polychloroprene and silicones. In an embodiment, a polymer is anelastomer.

“Conformable” refers to a device, material or substrate which has abending stiffness that is sufficiently low to allow the device, materialor substrate to adopt any desired contour profile, for example a contourprofile allowing for conformal contact with a surface having a patternof relief features. In certain embodiments, a desired contour profile isthat of a tissue in a biological environment.

“Conformal contact” refers to contact established between a device and areceiving surface. In one aspect, conformal contact involves amacroscopic adaptation of one or more surfaces (e.g., contact surfaces)of a device to the overall shape of a surface. In another aspect,conformal contact involves a microscopic adaptation of one or moresurfaces (e.g., contact surfaces) of a device to a surface resulting inan intimate contact substantially free of voids. In an embodiment,conformal contact involves adaptation of a contact surface(s) of thedevice to a receiving surface(s) such that intimate contact is achieved,for example, wherein less than 20% of the surface area of a contactsurface of the device does not physically contact the receiving surface,or optionally less than 10% of a contact surface of the device does notphysically contact the receiving surface, or optionally less than 5% ofa contact surface of the device does not physically contact thereceiving surface. In an embodiment, a method of the invention comprisesestablishing conformal contact between a conformal transfer device andone or more single crystalline inorganic semiconductor structures, oneor more dielectric structures and/or one or more metallic conductorstructures, for example, in a microtransfer printing process, such asdry transfer contact printing.

“Young's modulus” is a mechanical property of a material, device orlayer which refers to the ratio of stress to strain for a givensubstance. Young's modulus may be provided by the expression:

$\begin{matrix}{{E = {\frac{({stress})}{({strain})} = {\left( \frac{L_{0}}{\Delta \; L} \right)\left( \frac{F}{A} \right)}}},} & (I)\end{matrix}$

where E is Young's modulus, L₀ is the equilibrium length, ΔL is thelength change under the applied stress, F is the force applied, and A isthe area over which the force is applied. Young's modulus may also beexpressed in terms of Lame constants via the equation:

$\begin{matrix}{{E = \frac{\mu \left( {{3\lambda} + {2\mu}} \right)}{\lambda + \mu}},} & ({II})\end{matrix}$

where λ and μ are Lame constants. High Young's modulus (or “highmodulus”) and low Young's modulus (or “low modulus”) are relativedescriptors of the magnitude of Young's modulus in a given material,layer or device. In some embodiments, a high Young's modulus is largerthan a low Young's modulus, preferably about 10 times larger for someapplications, more preferably about 100 times larger for otherapplications, and even more preferably about 1000 times larger for yetother applications. In an embodiment, a low modulus layer has a Young'smodulus less than 100 MPa, optionally less than 10 MPa, and optionally aYoung's modulus selected from the range of 0.1 MPa to 50 MPa. In anembodiment, a high modulus layer has a Young's modulus greater than 100MPa, optionally greater than 10 GPa, and optionally a Young's modulusselected from the range of 1 GPa to 100 GPa. In an embodiment, a deviceof the invention has one or more components, such as substrate,encapsulating layer, inorganic semiconductor structures, dielectricstructures and/or metallic conductor structures, having a low Young'smodulus. In an embodiment, a device of the invention has an overall lowYoung's modulus.

“Inhomogeneous Young's modulus” refers to a material having a Young'smodulus that spatially varies (e.g., changes with surface location). Amaterial having an inhomogeneous Young's modulus may optionally bedescribed in terms of a “bulk” or “average” Young's modulus for theentire material.

“Low modulus” refers to materials having a Young's modulus less than orequal to 10 MPa, less than or equal to 5 MPa or less than or equal to 1MPa.

“Bending stiffness” is a mechanical property of a material, device orlayer describing the resistance of the material, device or layer to anapplied bending moment. Generally, bending stiffness is defined as theproduct of the modulus and area moment of inertia of the material,device or layer. A material having an inhomogeneous bending stiffnessmay optionally be described in terms of a “bulk” or “average” bendingstiffness for the entire layer of material.

Transient devices and methods of making and using the devices will nowbe described with reference to the figures. For clarity, multiple itemswithin a figure may not be labeled and the figures may not be drawn toscale.

FIGS. 1A-1D provide schematic diagrams illustrating side views oftransient electronic devices of the invention. FIGS. 1A and 1B aredirected to transient electronic devices having a multilayer encapsulantlayer comprising a selectively removable inorganic material incombination with a barrier layer or electrically insulating layer. FIGS.1C and 1D are directed to a transient electronic device having amultilayer substrate comprising a selectively removable inorganicmaterial in combination with a barrier layer or electrically insulatinglayer.

In FIG. 1A, transient electronic device 100A comprises substrate 105supporting, directly or indirectly, one or more inorganic semiconductorcomponents, one or more metallic conductor components or one or moreinorganic semiconductor components and one or more metallic conductorcomponents 110, which in some embodiments comprise semiconductor devicesor semiconductor device components. Encapsulant layer 115A is providedso as to completely or partially encapsulate the inorganic semiconductorcomponents and/or metallic conductor components 110, for example byencapsulating at least 20%, 50%, 70% or 90% of the area or volume of theinorganic semiconductor components and/or metallic conductor components110. As shown in FIG. 1A, encapsulant layer 115A is a multilayerstructure comprising an interior layer 120, comprising a barrier layeror electrically insulating layer, and an exterior layer 125 comprising aselectively removable inorganic material, such as an inorganic thinfilm, foil or coating. In an embodiment, for example, interior layer 120is an electrically insulating layer preventing electrical contactbetween exterior layer comprising a selectively removable inorganicmaterial 125 and the underlying inorganic semiconductor componentsand/or metallic conductor components 110. In an embodiment, for example,exterior layer 125 comprises a metal foil or metal oxide layer having apreselected transience profile, wherein at least partial removal of theexterior layer 125 in response to an external or internal stimulus atleast partially exposes the inorganic semiconductor components and/ormetallic conductor components 110, for example, to the internal orexternal stimulus and/or to an external environment.

In FIG. 1B, transient electronic device 100B comprises substrate 105supporting, directly or indirectly, one or more inorganic semiconductorcomponents, one or more metallic conductor components or one or moreinorganic semiconductor components and one or more metallic conductorcomponents 110, which in some embodiments comprise semiconductor devicesor semiconductor device components. Encapsulant layer 1158 is providedso as to completely or partially encapsulate the inorganic semiconductorcomponents and/or metallic conductor components 110, for example byencapsulating at least 20%, 50%, 70% or 90% of the area or volume of theinorganic semiconductor components and/or metallic conductor components110. As shown in FIG. 1B, encapsulant layer 115B is a multilayerstructure comprising an interior layer 120 comprising a barrier layer,or electrically insulating layer, and an intermediate layer 125comprising a selectively removable inorganic material, such as aninorganic thin film, foil or coating and an exterior layer 130comprising a barrier layer or electrically insulating layer. In anembodiment, for example, interior layer 120 is an electricallyinsulating layer preventing electrical contact between intermediatelayer comprising a selectively removable inorganic material 125 and theunderlying inorganic semiconductor components and/or metallic conductorcomponents 110. In an embodiment, for example, exterior layer 130 is abarrier layer substantially impermeable to an external composition, suchas an external solvent (e.g., water, biofluid, etc.). In an embodiment,for example, intermediate layer 125 comprises a metal foil or metaloxide layer having a preselected transience profile, wherein at leastpartial removal of the intermediate layer 125 and interior layer 120 inresponse to an external or internal stimulus at least partially exposesthe inorganic semiconductor components and/or metallic conductorcomponents 110, for example, to the internal or external stimulus and/orto an external environment.

In FIG. 1C, transient electronic device 200A comprises substrate 215Asupporting, directly or indirectly, one or more inorganic semiconductorcomponents, one or more metallic conductor components or one or moreinorganic semiconductor components and one or more metallic conductorcomponents 210, which in some embodiments comprise semiconductor devicesor semiconductor device components. Encapsulant layer 220 is provided soas to completely or partially encapsulate the inorganic semiconductorcomponents and/or metallic conductor components 210, for example byencapsulating at least 20%, 50%, 70% or 90% of the area or volume of theinorganic semiconductor components and/or metallic conductor components210. As shown in FIG. 10, substrate 215A is a multilayer structurecomprising an interior layer 230, comprising a barrier layer orelectrically insulating layer, and an exterior layer 205 comprising aselectively removable inorganic material, such as an inorganic thinfilm, foil or coating. In an embodiment, for example, interior layer 230is an electrically insulating layer preventing electrical contactbetween exterior layer comprising a selectively removable inorganicmaterial 205 and the inorganic semiconductor components and/or metallicconductor components 210. In an embodiment, for example, exterior layer205 comprises a metal foil or metal oxide layer having a preselectedtransience profile, wherein at least partial removal of the exteriorlayer 205 in response to an external or internal stimulus at leastpartially exposes the inorganic semiconductor components and/or metallicconductor components 210, for example, to the internal or externalstimulus and/or to an external environment.

In FIG. 1D, transient electronic device 200B comprises substrate 215Bsupporting, directly or indirectly, one or more inorganic semiconductorcomponents, one or more metallic conductor components or one or moreinorganic semiconductor components and one or more metallic conductorcomponents 210, which in some embodiments comprise semiconductor devicesor semiconductor device components. Encapsulant layer 220 is provided soas to completely or partially encapsulate the inorganic semiconductorcomponents and/or metallic conductor components 210, for example byencapsulating at least 20%, 50%, 70% or 90% of the area or volume of theinorganic semiconductor components and/or metallic conductor components210. As shown in FIG. 10, substrate 215B is a multilayer structurecomprising an interior layer 230A comprising a barrier layer orelectrically insulating layer, and an intermediate layer 205 comprisinga selectively removable inorganic material, such as an inorganic thinfilm, foil or coating and an exterior layer 230B comprising a barrierlayer or electrically insulating layer. In an embodiment, for example,interior layer 230A is an electrically insulating layer preventingelectrical contact between intermediate layer comprising a selectivelyremovable inorganic material 205 and the inorganic semiconductorcomponents and/or metallic conductor components 210. In an embodiment,for example, exterior layer 230B is a barrier layer substantiallyimpermeable to an external composition, such as an external solvent(e.g., water, biofluid, etc.). In an embodiment, for example,intermediate layer 205 comprises a metal foil or metal oxide layerhaving a preselected transience profile, wherein at least partialremoval of the intermediate layer 205 and interior layer 230A inresponse to an external or internal stimulus at least partially exposesthe inorganic semiconductor components and/or metallic conductorcomponents 210, for example, to the internal or external stimulus and/orto an external environment.

Example 1 Inorganic Substrates and Encapsulation Layers for TransientElectronics Background and Motivation

This example demonstrates a new class silicon-based electronic devicesthat are physically transient, for example, in the sense that theydissolve or otherwise transform at controlled rates when exposed towater in the environment or the body[1]. In some embodiments, thesesystems comprise transient materials, such as magnesium for metalelectrodes and interconnects, MgO and/or SiO₂ for gate and interlayerdielectrics, and single crystal silicon nanomembranes (Si NMs) forsemiconductors. In all cases, extensive engineering studies of the keyproperties, including dissolution mechanisms[2], for each material areimportant for device engineering. On-going research indicates theability to enhance/control the dissolution rates of transient componentsvia control over the morphology and chemical compositions of the variousfunctional layers. Additionally, the properties of the aqueousenvironments can have a strong influence. Initial experiments on Si NMs,for example, reveal the dependence of dissolution rates on variousaqueous environments, such as blood, sea water, serum, tap water, andsimulated body solution with different pH levels. Similar studies onvarious candidates for the conductive layers, for instance, Mg alloy(AZ31B), iron (Fe), molybdenum (Mo), tungsten (W) and zinc (Zn),establish their utility and range of uses.

Besides these functional layers, encapsulation and substrate materialsplay important roles in these systems because their transientcharacteristics may also define the operational lifetimes. Silk, otherbiomaterials and synthetic polymers are of strong interest, but theirinability to serve as completely impermeable water barriers, withoutdimensional change associated with swelling, represent dauntingtechnical challenges. Inorganic materials may provide compellingalternatives. A natural, attractive candidate as an encapsulant and/orcomponent of a layered substrate construct is SiO₂ deposited usingvarious conditions in PECVD to control density and, therefore,dissolution rate. Another promising related possibility is spin-on-glass(SOG), due to its solution processability and excellent planarizationproperties. Metal foils have potential as mechanically tough, rugged butflexible substrates. This example describes use of these materials assubstrates and encapsulation layers.

The present example highlights the significance of establishing (a)dissolution rates for various inorganic materials relevant toencapsulation layers and substrates for transient electronic systems,and (b) demonstration vehicles for the use of these materials inelectronic devices with practical ranges of transience times. Thepresent example describes (1) the study of the kinetics of dissolutionfor silicon, silicon oxide, spin-on-glass, and metals in varioussolutions, (2) design and demonstration of an inorganic-based substratesystem and encapsulation strategy using these materials, and (3)integration of simple transient electronic components (resistors,inductors, transistors) onto these substrates, with encapsulation, todemonstrate function.

Dissolution Rates for Inorganic Materials as Substrates andEncapsulation Layers Deposited and Grown Layers of Silicon Dioxide(SiO₂)

Silicon dioxide (SiO₂) serves as an example material option for the gateand interlayer dielectrics of previously reported transient electronicdevices[1]. An ability to control the rate of dissolution in thismaterial, and to exploit it in substrates and encapsulation layers formsa focus of this example. FIG. 2 shows that a thin film of SiO₂ depositedby plasma enhanced chemical vapor deposition (PECVD) dissolves in PBSsolution at room temperature and physiological temperature,respectively, over the course of weeks. The chemical mechanisms here arerelated to those of single crystalline silicon, i.e. silicon oxidereacts water via hydrolysis to form silicic acid (Si(OH)₄). A key recentfinding is that the dissolution rates depend strongly on depositionconditions. This example explores the dissolution of PECVD SiO₂ formedat various temperatures between 200 and 500° C., as well as wet and drythermally grown oxides (1100° C.; data in FIG. 3). Preliminary findingsshow that thermal oxide has extremely slow dissolution compared to lowtemperature PECVD material. These two examples bracket a broad range oftransience times that can be accessed in this single material system,thereby highlighting its potential value as an encapsulation layer, oras a component of a layered substrate construct (see, below).

Bulk Foils and Thin Film Coatings of Metals (Mg, Mg Alloy, Fe, W and Zn)

Conductive materials are essential for electrodes and interconnects intransient electronics. This example shows, however, that conductivematerials, for example in the form of foils or coatings, also provide animportant class of materials for substrates and/or encapsulation layerswhen combined with insulating layers to avoid unwanted electricaleffects. Systematic fundamental studies of dissolution kinetics ofvarious metals, both as bulk foils and thin film coatings, in biologicalenvironments provide important guidelines on selecting metals for thesepurposes. Six metals are of interest: magnesium (Mg), magnesium alloy(AZ31 B with 3 wt % aluminum and 1 wt % zinc), tungsten (W), molybdenum(Mo), zinc (Zn) and iron (Fe). Preliminary dissolution measurements inde-ionized (DI) water and simulated bio-fluid (Hank's solution, pH 7.4)at room temperature appear in FIG. 4. Here, films with thicknesses of150 nm or 300 nm were formed by electron beam (E-beam) evaporation (Fe,Mo) or magnetron sputtering (Mg, Mg alloys, Zn and W). In general, W andFe exhibit much slower degradation rates (˜few days) compared to Mg, Mgalloys and Zn (<few hours) due to the non-protective nature of theirhydrolysis products, namely magnesium oxide and zinc oxide respectively.Resistance changes in Fe appear very gradually, due to the formation ofa relatively protective iron oxide layer. Compared to sputtered W films,CVD W possesses a much lower resistivity and slower dissolution rate inDI water, making it ideal for long term transience. A reactive diffusionmodel can capture the trends for Mg, Mg alloys, Zn and W (solid lines inFIG. 4), thereby providing the ability to predict transience times as afunction of thin film thickness, pH, and other parameters. Based onthese results, metals combined with suitably processed SiO₂ enable thedegradation times that span a desired range, from minutes to months, andpossibly longer. In the form of foils and layered assemblies, thesematerials are attractive as flexible substrates, as described next.

Inorganic Substrate Structures for Transient Electronics

Inorganic substrates based on coated metal foils could represent anattractive alternative to silk-based biopolymers, or synthetic polymers.A schematic illustration of one possibility appears in FIG. 5. Thestructure simply utilizes a metal foil (e.g. Mg foil, 5˜10 urn thick) asa supporting material with films of spin cast SOG as electricallyinsulating layers and water barriers on top and bottom. The foil impartsa level of mechanical robustness that is not present in the SOG filmsalone. Additional layers of PECVD SiO₂ and/or metals can be added to thestructure to enhance the barrier properties and to minimize probabilityfor electrical leakage pathways, thereby offering the possibility toextend the transience times. A variety of combinations of layeredstructures based on the materials described in the previous sectioncreates a rich design space.

Demonstration Vehicles for Transient Electronics Based on InorganicSubstrates and Encapsulants

To evaluate practical performance of encapsulants and substratestructures outlined in the previous sections, test vehicles ranging fromserpentine resistors and inductors to Si NM transistors may be built.Electrical evaluation of these components may be performed as a functionof time for complete immersion in DI water and PBS at physiologicalconditions. The kinetics associated with transience in function may bestudied, and correlated to the choice of materials and layeredstructures.

REFERENCES

-   1. S.-W. Hwang, H. Tao, D.-H. Kim, H. Cheng, J.-K. Song, E.    Rill, M. A. Brenckle, B. Panilaitis, S. M. Won, Y.-S. Kim, Y. M.    Song, K. J. Yu, A. Ameen, R. Li, Y. Su, M. Yang, D. L. Kaplan, M. R.    Zakin, M. J. Slepian, Y. Huang, F. G. Omenetto and J. A. Rogers, “A    Physically Transient Form of Silicon Electronics,” Science 337,    1640-1644 (2012).-   2. R. Li, H. Cheng, Y. Su, S.-W. Hwang, L. Yin, H. Tao, M. A.    Brenckle, D.-H. Kim, F. G. Omenetto, J. A. Rogers and Y. Huang, “An    Analytical Model of Reactive Diffusion for Transient Electronics,”    Advanced Functional Materials, ASAP (2013). DOI:    10.1002/adfm.201203088

Example 2 Inorganic Substrates and Encapsulation Layers for TransientElectronics

FIG. 6 shows dissolution kinetics of SiO₂ in aqueous solution atdifferent pH and temperature (1) SiO₂ thermally grown by dry or wetoxidation, (2) SiO₂ deposited by plasma enhanced chemical vapordeposition and (3) SiO₂ deposited by electron beam evaporation.Calculated (lines) and experimental (symbols) dissolution rates ofsilicon oxides in buffer solution at different pH (black, pH 7.4; red,pH 8; blue, pH 10; magenta, pH 12) at room (left) and physiological(right, 37° C.) temperature. The thickness was measured by spectroscopicellipsometry. There was no difference is dissolution rates betweenthermally grown SiO₂ grown by the dry or wet oxidation method.

FIG. 7A shows measured data (symbols) and numerical fits (lines) forpH-dependent dissolution kinetics of oxides (black, tg-oxide by dryoxidation; red, tg-oxide by wet oxidation; blue, PECVD oxide; magenta,E-beam oxide) at room temperature and 37° C. Higher pH concentrationincreases the possibility of reaction between Si-0 and OH⁻, andtherefore increases the dissolution rate. Quartz and amorphous silicashowed the same trend in the literature.[1]

FIG. 7B shows SiO₂ film property dependency exhibited as film densityversus dissolution rate. Low density films have more chances to meetreaction species, which increases dissolution rate. Low density filmsalso have fewer atoms per layer, which causes the dissolution rate interms of thickness to decrease faster.

FIG. 8 shows a dissolution study of SiN_(X). SiN_(x) is oxidized to SiO₂in a first step and converted to silicic acid in a second step.[2] Finalproducts include NH₃, which the human body produces about 4 g of daily.The same estimated NH₃ amount as a device less than or equal to 1 mg.

FIG. 9A shows measured data (symbols) and numerical fits (lines) forpH-dependent dissolution kinetics of nitrides (black, low pressure CVD;red, PECVD-LF; blue, PECVD-HF) at room temperature and 37° C. FIG. 9Bshows SiN_(x) film property dependency exhibited as film density versusdissolution rate.

FIG. 10 shows dissolution kinetics for different oxides immersed invarious aqueous solutions. A) Bovine serum (pH ˜7.4) at 37° C. (black,tg-oxide by dry oxidation; red, tg-oxide by wet oxidation; blue, PECVDoxide; magenta, E-beam oxide), B) sea water (pH ˜7.8) at RT (black,tg-oxide by dry oxidation; red, tg-oxide by wet oxidation; blue, PECVDoxide; magenta, E-beam oxide), C) Bovine serum (pH ˜7.4) at 37° C.(black, LPCVD nitride; red, PECVD nitride with LF mode; blue, PECVDnitride with HF mode), D) sea water (pH ˜7.8) at RT (black, LPCVDnitride; red, PECVD nitride with LF mode; blue, PECVD nitride with HFmode). Dissolution rates of SiO₂/SiN_(x) in bovine serum and sea waterare ˜10 and ˜4 times faster than buffer solution under the sameconditions. Likely, the cations in bovine serum and sea water (K⁺, Na⁺,Ca²⁺ and Mg²⁺) accelerate the dissolution rate of SiO₂.

FIG. 11 shows the curing mechanism for spin-on-glass and dissolutionstudies of spin-on-glass encapsulation layers cured at varioustemperatures and times. Silicate based spin-on glass (SOG) isdissolvable, and dissolution rate can be controlled by adjusting curingconditions and thickness. Increasing curing temperature and time givesslower dissolution rates due to fewer —OH bonds in the cured SOG.Combining SOG with other oxide layers improves inorganic encapsulationproperties.

FIG. 12 shows pH dependent dissolution studies of amorphous silicon(a-Si), polycrystalline silicon (p-Si) and SiGe. The dissolution rate ofa-Si/p-Si is similar to single crystalline Si (100), which means thedissolution of Si does not depend on type of Si. Dissolution of SiGe(8:2 wt %) is slightly slower than single crystalline Si because SiGecomprises mostly Si—Si bonds with relatively few Si—Ge bonds (<10%).

FIG. 13 shows electrical dissolution rates and thicknesses of sputterdeposited Mg, Mg alloy (AZ31B, Al 3%, Zn 1%), Zn, Mo, W, CVD depositedW, and E-beam evaporated Fe in DI water and Hanks' solution with pH 5-8.

FIG. 14 shows current versus voltage plots for devices containingtransient metal components. N-type MOSFETs built with transient metalthin films exhibit on/off ratios >10⁴ and mobilities ˜250 cm²/Vs.Functionality degradation in DI water was measured without encapsulationat V_(d)=0.2 V.

FIG. 15 shows photographs of the dissolution of a transient transistorarray on a biodegradable metal foil.

FIG. 16 provides plots of dissolution kinetics of various metal foils(Mo, Zn, Fe, W) under physiological conditions (PBS, pH 7.4, 37° C.).

FIG. 17 provides a schematic of a fabrication strategy using metal foilsinvolving: 1) Lamination of metal foil on a carrier substrate (e.g.,PDMS coated on glass), 2) fabrication of a transistor array directly onthe metal foil, and 3) peeling of the device from the carrier substrate.

FIG. 18 demonstrate the use of inorganic substrates. For example, metalfoils, such as Fe with a thickness of 5 μm or Mo with a thickness of 10μm, may be used as substrates to support device fabrication. Devices mayalso be inorganic, e.g. Mg-based transitors. The entire array may beflexible, as shown.

FIG. 19 provides schematic illustrations of encapsulation methods fortransient electronic devices, showing defects (e.g. pinholes) covered bya bilayer of SiO₂/Si₃N₄; ALD provides a defect-free layer. Defects, suchas pinholes, are the primary cause of leakage of vapors or fluids inencapsulation with PE-CVD SiO₂ and SiN_(x). Multilayer structures ofboth silicon oxides and silicon nitrides can reduce such defects. An ALDlayer has fewer defects than a PE-CVD layer.

FIG. 20 shows measurements of changes in resistance of Mg traces (˜300nm thick) encapsulated with different materials and thicknesses whileimmersed in deionized (DI) water at room temperature. A single layer ofALD SiO₂ (orange, 20 nm), PECVD SiO₂ (black, 1 μm) and PECVD-LF Si₃N₄(red, 1 μm), a double layer of PECVD SiO₂/PECVD-LF Si₃N₄ (blue, 500/500nm), PECVD SiO₂/ALD SiO₂ (magenta, 500/20 nm), PECVD-LF Si₃N₄/ALD SiO₂(purple, 500/20 nm), and a triple layer of PECVD SiO₂/PECVD-LF Si₃N₄(Cyan, 200/200/200/200/100/100 nm) were used for the encapsulation.

FIG. 21 shows a series of micrographs of a serpentine trace of Mg(initially ˜300 nm thick) during dissolution in DI water at roomtemperature. Dissolution begins from local defects, then rapidlypropagates outward.

FIG. 22 shows a demonstration of the electrical properties of electronicdevices fabricated on metal foils. (A) Transistor array on Fe foil (˜10μm thick), (B) Diode array on Zn foil (˜10 μm thick), (C) Capacitorarray on Mo foil (˜10 μm thick), (D) Inductor array on Mo foil (˜10 μmthick). Electronic devices were successfully fabricated on biodegradablemetal substrates (Fe, W, Mo, Zn, Mg). The performance of transientdevices on metal substrates is comparable to devices fabricated onnon-transient substrates.

FIG. 23 shows transience of transient devices on inorganic substrateswith inorganic encapsulation. (A) Transistor on Mo foil with MgOencapsulation (˜800 nm), (B) Diode on Mo foil with MgO encapsulation(˜800 nm), (C) Capacitor on Mo foil with MgO encapsulation (˜800 nm),(D) Inductor on Mo foil with MgO encapsulation.

FIG. 24 shows a sample structure for a dissolution test of single waferSiGe (Ge) with atomic force microscopy (AFM). (a) Schematic illustrationof test structure: array of square holes (3 μm×3 μm×20 nm) of PECVD SiO₂mask on SiGe single wafer. (b) AFM topographical images and c) profilesof SiGe, at different stages of dissolution in buffer solution (pH 10)at 37° C.

FIG. 25 shows dissolution kinetics of various semi-conductors in variousbuffer solutions, with different pH at room and physiologicaltemperatures. (a) polycrystalline silicon, (b) amorphous silicon, (c)silicon-germanium and (d) germanium.

FIG. 26 shows dissolution kinetics of different types of silicon invarious aqueous solutions. (a) Tap water (pH ˜7.8), deionized water (DI,pH ˜8.1) and spring water (pH ˜7.4), (b) Coke (pH ˜2.6), (c) milk (pH˜6.4) at room temperature, (d) bovine serum (pH ˜7.4) at room and 37°C., and (e) sea water (pH ˜7.8) at room temperature. (f) Changes inresistance of a meander trace formed from a phosphorous dopedpolycrystalline and amorphous Si NM (˜35 nm) in phosphate buffersolution (pH 10) at 37° C.

FIG. 27 shows a thin film solar cell with fully transient materials.(a), (b) Image and structure of amorphous Si based photovoltaic cellarray on degradable substrate. (c) Performance of unit cell of solarcells. (d) Electrical transience behavior of a-Si diode and (e)transience of performance of solar cell.

REFERENCES

-   [1] K. G. Knauss & T. J. Wolery, Geochim. Cosmochim. Acta 52, 43-53    (1998). W. A. House & L. A. Hickinbotham, J. Chem. Soc. Faraday,    Trans. 88, 2021-2026 (1992).-   [2] E. Laarz et al., J. Am. Ceram. Soc. 83, 2394-2400 (2000).    Toxicological Profile for Ammonia, published by the U.S. Department    of Health and Human Services, ATSDR (2004).

Example 3 Dissolution Behaviors and Applications of Silicon Oxides andNitrides in Transient Electronics Background and Motivation

Silicon oxides and nitrides are key materials for dielectrics andencapsulations in a class of silicon-based high performance electronicsthat has the ability to completely dissolve in a controlled fashion withprogrammable rates, when submerged in bio-fluids and/or relevantsolutions. This type of technology, referred to as ‘transientelectronics’, has potential applications in biomedical implants,environmental sensors and other envisioned areas. The results presentedhere provide comprehensive studies of transient behaviors of thin filmsof silicon oxides and nitrides in diverse aqueous solutions at differentpH scales and temperatures. The kinetics of hydrolysis of thesematerials primarily depends on not only pH levels/ion concentrations ofsolutions and temperatures, but also morphology and chemistry of filmsdetermined by the deposition methods and conditions. Encapsulationstrategies with a combination of layers demonstrate enhancement of thelifetime of transient electronic devices, by reducing water/vaporpermeation through the defects.

INTRODUCTION

Materials for insulation, passivation and encapsulation inmicroelectronics are critically important for proper operation of thedevices. Silicon oxides and nitrides are in widespread use not only fordigital and analog circuits but also for thin film display electronicsand others, due to their excellent properties as gate and interlayerdielectrics, passivation coatings,^([1-3]) and barriers against waterpenetration.^([4,5]) This paper explores the materials aspects of use ofthese films in a different, emerging class of electronics, whosedefining characteristic is solubility in water, with environmentally andbiologically benign end products. This type of technology, sometimesreferred to as one type of transient electronics, could be important fortemporary biomedical implants, resorbable sensors and monitors for theenvironment, ‘green’ disposable consumer devices and other systems thatare not well served by conventional electronics, which last for decadesand involve biologically and environmentally harmful materials. Initialdemonstrations relied either on miniaturized, non-degradable inorganiccomponents integrated with resorbable silk substrates and encapsulatinglayers,^([6.7]) or on synthetic and/or nature-inspired organic activeand passive materials.^([8-10]) An important advance followed from theobservation that monocrystalline, device-grade silicon in ultrathinforms (i.e. nanomembranes), can dissolve, at various rates, in differenttypes of biofluids as well as in seawater and other naturally occurringforms of water, all of relevance to envisioned applications. The endproduct, silicic acid, is biocompatible and environmentally benign atthe low levels of concentration that are associated with smallnanomembranes of silicon. Representative examples of demonstrationdevices include high performance complementary metal-oxide-semiconductor(CMOS) transistors and simple circuits, solar cells, strain/temperaturesensors, digital imaging devices, wireless power scavenging systems andothers.^([11-13]) Additional inorganic semiconductor options includeZnO, of interest in part due to its piezoelectric properties, fortransient mechanical energy harvesters, actuators and others.^([14]) Inmost of these examples, MgO, which undergoes hydrolysis to Mg(OH)₂,serves as the dielectric and encapsulation layer. Initial observationssuggested that SiO₂ might provide another option. Here, we study thismaterial in detail, and also provide evidence that SiN_(x) representsanother alternative.

Dissolution Studies of Different Types of Oxides

Previous work on bulk materials establishes that the mechanism forhydrolysis of silicon oxides is SiO₂+2H₂O→Si(OH)₄.^([15-17]) Because OH⁻initiates this reaction, the concentration of OH⁻ (pH of solution)strongly influences the dissolution rate, as observed in studies of thedissolution kinetics of quartz and amorphous silica.^([15-18]) Here, weexamine materials in forms and with chemistries widely utilized in thesemiconductor industry, as thin films grown/deposited using standard orslightly modified techniques. The results reveal essential aspects ofhydrolysis in such cases, including the influence of morphology andchemistry, as defined by the conditions and methods for deposition. Toexamine the dependence of the dissolution rate on pH and type of oxide,systematic studies were performed in buffer solutions with pH between7.4 to 12, and at different temperatures. Three different classes ofmaterials were examined—thin films of oxides formed by 1) growth usingdry (O₂ gas) and wet (H₂O vapor) thermal oxidation (tg-oxide), 2) plasmaenhanced chemical vapor deposition (PECVD oxide) and 3) electron-beam(E-beam oxide) evaporation.

Spectroscopic ellipsometry (J. A. Wooldman Co. Inc., USA) revealed thedissolution rate as a time dependent change in thickness. Atomic forcemicroscopy (AFM, Asylum Research MFP-3D, USA) provided information onthe surface topography as well as independent measurements of thickness.Test structures of PECVD and E-beam materials for AFM measurementsconsisted of arrays of isolated square films (3 μm×3 μm×100 nm)patterned on tg-oxide, whose dissolution rate is much slower than thatof other materials, as shown subsequently. FIG. 28 a presents aschematic illustration of a test structure, and an optical micrograph inthe inset. FIGS. 28 b and 28 c provide AFM images and thickness profilesat several stages of immersion in aqueous buffer solution (pH 12) at 37°C. (Additional AFM images appear in FIGS. 29 and 30). These resultsindicate that the oxides dissolve in a uniform fashion, without anysignificant change in surface topography, formation of flakes or othernon-ideal behaviors like those observed, for example, in transientmetals under similar conditions.^([19]) In all cases, samples wereimmersed in ˜50 mL of aqueous solutions, removed, rinsed and dried, andthen measured (spectroscopic ellipsometry; AFM). After measurements(total times of several hours), samples were placed back into freshsolutions. The solutions were replaced every other day. (The dissolutionrates, for all cases examined, did not change substantially for varioustime intervals for solution replacement (e.g. for every 1, 2, 4 or 7days).

FIG. 31 a-c and FIG. 6(1) provide the dissolution kinetics of tg-oxide(dry and wet oxidation), PECVD oxide and E-beam oxide in terms of thechange in thickness as a function of time in buffer solutions (pH 7.4 to12) at room temperature (RT) and 37° C. The tg-oxides and E-beam oxideexhibit the slowest and fastest rates, respectively, under the sameconditions. Four main factors affect the rate: temperature, pH and ioniccontent of the solutions, and chemical/morphological properties of thefilms. The dissolution rate of each oxide increases with temperature,with an expected Arrhenius dependence, consistent with previousstudies.^([17,20])

FIG. 31 d shows a linear dependence of the dissolution rate for eachtype of oxide in buffer solutions with different pH at (see more detailsat RT in FIG. 7), similar to related observations.^([15-17]) Therelationship can be written log r=a+n [pH], where r is the dissolutionrate, and a and n are constants (n=0.33 for quartz when r is inmol/m²s).^([16]) The values of n for the data in FIG. 31 d and FIG. 7are between 0.31 to 0.44 (at 37° C.) and 0.22 to 0.62 (at RT),respectively. The kinetics can also be influenced by the concentrationof ions in the solution.^([21,22]) As an example, bovine serum (pH ˜7.4)and sea water (pH-7.8) show rates that are ˜9 and ˜4 times higher thanthose observed at similar pH in buffer solution, respectively, likelydue to the presence of additional ions (ex. K⁺, Na⁺, Ca²⁺ and Mg²⁺) inthese liquids.^([21,22])

The dissolution rate can also be affected, of course, by the physicaland chemical properties of the films, which in turn depend ongrowing/deposition methods and conditions. Thermal oxide is known to beuniformly dense.^([23]) Oxide created by PECVD can show differentstoichiometries and densities, due to by-products from the SiH₄ sourcegas as it reacts with Si to form Si—H. Such effects can be particularlyimportant for low temperature deposition.^([24]) E-beam oxide formedfrom a pure source of SiO₂ (i.e. pellets) can involve nanoscalefragmentation during evaporation, which can potentially lead toalterations in the stoichiometry and reductions in density.^([25])

X-ray photoelectron spectroscopy (XPS) and X-ray reflectometry (XRR)reveal the stoichiometries, atomic bond configurations and densities.The tg-oxide (dry oxidation) and PECVD oxide have chemistries close toSiO₂ (i.e., Si:O=1:2), while the E-beam oxide is oxygen rich, atSiO_(2.2) (Si:O=1:2.2), as shown in Table 1.

TABLE 1 Atomic concentration of different silicon oxides measured byXPS. Carbon (C) and fluorine (F) are considered surface contamination.(%) Si O C F x (SiO_(x)) tg-SiO₂ (dry) 31.6 64.0 4.3 0.1 2.0 PECVD SiO₂31.5 63.5 3.6 1.4 2.0 E-beam SiO₂ 27.5 61.3 10.8 0.4 2.2

The Si 2P spectra (FIG. 32) indicate that the Si—O bond energies arealmost identical for the three oxides. FIG. 31 e and FIG. 33 show thedependence of the dissolution rate on the film density (˜2.3 g/cm³ fortg-oxides, ˜2.1 g/cm³ for PECVD oxide, ˜1.9 g/cm³ for E-beam oxide).Reduced density can enhance the ability of aqueous solutions to diffuseinto the material, thereby accelerating the hydrolysis reaction byincreasing the reactive surface area.^([11,19,26]) Previousresearch^([11,19,26]) suggests that a reactive. diffusion model cancapture some of the behaviors. A modified version of this model,assuming applicability of continuum physics, provides a simple,approximate means to incorporate the effect of density variationsassociated with porosity. Here, the concentration of water in the porousmaterial is first determined from the partial differential equation forreactive diffusion D_(e)∂²w/∂_(Z) ²−kw=∂w/∂t, where k and D_(e) are thereaction constant and the diffusivity in the porous media, respectively.Since the mass of the air pore is negligible compared with that of theporous material, the effective density ρ_(eff) of the porous material isrelated to the density ρ_(s) of the fully dense material as

$\begin{matrix}{{\rho_{eff} = {\frac{V_{s}}{V_{air} + V_{s}}\rho_{s}}},} & (1)\end{matrix}$

where V_(s) and V_(air) are the volumes of material and air pore,respectively. At time t=0, the air pores are filled with water, orw|_(l=0)=w₀(ρ_(s)−ρ_(eff))/ρ_(s)(0≦z<h₀). The water concentration isconstant at the top surface of the material w|_(z=h) ₀ =w₀ (w₀=1 g/cm³)and the water flux is zero at the bottom surface ∂w/∂z|_(z=0)=0. By themethod of separation of variables, the water concentration field can bewritten

$\begin{matrix}{{{w\left( {y,t} \right)} = {w_{0}\begin{Bmatrix}{\frac{\cosh\left( {\sqrt{\frac{{kh}_{0}^{2}}{D_{e}}}\frac{y}{h_{0}}} \right)}{\cosh \sqrt{\frac{{kh}_{0}^{2}}{D_{e}}}} +} \\{2\pi {\sum\limits_{n = 1}^{\infty}{{B_{n}\left( {- 1} \right)}^{n}\left( {n - \frac{1}{2}} \right)^{{- {\lbrack{\frac{{kh}_{0}^{2}}{D_{e}} + {{({n - \frac{1}{2}})}^{2}\pi^{2}}}\rbrack}}\frac{D_{e}t}{h_{0}^{2}}}{\cos \left\lbrack {\left( {n - \frac{1}{2}} \right)\pi \; \frac{y}{h_{0}}} \right\rbrack}}}}\end{Bmatrix}}},} & (2)\end{matrix}$

where B_(n) is

$\begin{matrix}{B_{n} = {\frac{1}{\frac{{kh}_{0}^{2}}{D_{e}} + {\left( {n - \frac{1}{2}} \right)^{2}\pi^{2}}} + {\frac{\frac{\rho_{eff}}{\rho_{s}} - 1}{\left( {n - \frac{1}{2}} \right)^{2}\pi^{2}}.}}} & (3)\end{matrix}$

When one mole of material reacts with q moles of water, then integrationof materials dissolved at each location through the thickness and overtime leads to an expression for the remaining thickness h, normalized byits initial thickness h₀ as

$\begin{matrix}{\frac{h}{h_{0}} = {1 - {\frac{w_{0}M}{q\; \rho_{eff}M_{H_{2}O}}\frac{{kh}_{0}^{2}}{D_{e}}{\left\{ {{\frac{D_{e}t}{h_{0}^{2}}\frac{\tanh \sqrt{\frac{{kh}_{0}^{2}}{D_{e}}}}{\sqrt{\frac{{kh}_{0}^{2}}{D_{e}}}}} - {2{\sum\limits_{n = 1}^{\infty}{B_{n}\frac{1 - ^{{- {\lbrack{\frac{{kh}_{0}^{2}}{D_{e}} + {{({n - \frac{1}{2}})}^{2}\pi^{2}}}\rbrack}}\frac{D_{e}t}{h_{0}^{2}}}}{\left\lbrack {\frac{{kh}_{0}^{2}}{D_{e}} + {\left( {n - \frac{1}{2}} \right)^{2}\pi^{2}}} \right\rbrack}}}}} \right\}.}}}} & (4)\end{matrix}$

The effective diffusivity of water in a porous medium is linearlyproportional to the pores available for the transport, which isequivalent to the air fraction in the porous medium

$\begin{matrix}{{D_{e} \propto \frac{V_{air}}{V_{air} + V_{s}}} = {\frac{\rho_{s} - \rho_{eff}}{\rho_{s}}.}} & (5)\end{matrix}$

The density of SiO₂ is 2.33 g/cm³, 2.10 g/cm³ and 1.90 g/cm³ for thecase of thermally grown, PECVD and E-beam oxides, respectively. If SiO₂with a density of 2.34 g/cm³ has a diffusivity of 8×10⁻¹⁶ cm²/s at bodytemperature, then the diffusivities for PECVD SiO₂ and E-beam SiO₂ canbe calculated from Equation (5) as 1.6×10⁻¹⁴ cm²/s and 2.92×10⁻¹⁴ cm²/s.Reaction constants are fitted to the experimental data and thedissolution rate, −dh/dt, is then estimated from

$\begin{matrix}{{{- \frac{h}{t}} = {\frac{w_{0}M}{q\; \rho_{eff}M_{H_{2}O}}{kh}_{0}\left\{ {\frac{\tanh \sqrt{\frac{{kh}_{0}^{2}}{D_{e}}}}{\sqrt{\frac{{kh}_{0}^{2}}{D_{e}}}} - {2{\sum\limits_{n = 1}^{\infty}{B_{n}^{{- {\lbrack{\frac{{kh}_{0}^{2}}{D_{e}} + {{({n - \frac{1}{2}})}^{2}\pi^{2}}}\rbrack}}\frac{D_{e}t}{h_{0}^{2}}}}}}} \right\}}},} & (6)\end{matrix}$

which can be simplified to

$\begin{matrix}{{- \frac{h}{t}} = {\frac{w_{0}M}{q\; \rho_{eff}M_{H_{2}O}}{kh}_{0}{\frac{\tan \sqrt{\frac{{kh}_{0}^{2}}{D_{e}}}}{\sqrt{\frac{{kh}_{0}^{2}}{D_{e}}}}.}}} & (7)\end{matrix}$

In FIG. 31 a-c, the reaction constants (k) are 1.7×10⁻⁹ (tg-oxide withdry oxidation), 1.6×10⁻⁸ (PECVD oxide), and 1.3×10⁻⁹ (E-beam oxide) s⁻¹in buffer solution with pH 7.4 at 37° C. The results suggest thatdensity influences the dissolution rate not only through changes inrates for diffusion into the material, but also through differences inreactivity. One possibility is that dissolution can occur not just at amolecular level, but also through removal of nanoscale pieces ofmaterial that might be released from the film as narrow regions of theporous matrix disappear by hydrolysis. Careful transmission electronmicroscopy (TEM, JEOL 2010F, USA) studies (FIG. 34) suggest, however,that the porous structures in the PECVD and E-beam oxides do not involvevoids with dimensions larger than one or two nanometers. AFM observationof surfaces with sub-nanometer roughness (average roughness <0.4 nm,FIG. 35) throughout the course of the dissolution process also supportsthe notion that the film disappears uniformly and gradually, at themolecular level, without the release of pieces of material. Additionalwork is necessary to uncover an atomic level understanding of thedependence of reactivity on density.

Dissolution Studies of Various Classes of Nitrides

Studies of the dissolution kinetics of silicon nitrides were performedin procedures and under conditions similar to those for the siliconoxides. Silicon nitride hydrolyzes in aqueous solution in two steps: (1)oxidation into silicon oxide (Si₃N₄+6H₂O→3SiO₂+4NH₃) and (2) hydrolysisof silicon oxide (SiO₂+2H₂O→Si(OH)₄), where the overall reaction isSi₃N₄+12H₂O→3Si(OH)₄+4NH₃.^([27-29]) Because silicon dioxide serves asan intermediate product in these reactions, the dependence of rate on pHmight be expected to be similar to that observed in the oxides. Lowpressure chemical vapor deposition (LPCVD) and PECVD techniques wereused to form the silicon nitrides studied here. For PECVD nitrides, twodifferent frequency modes were employed to vary the properties of thefilms, including residual stress. Spectroscopic ellipsometry revealedthe changes in thickness of films deposited on silicon substrates.

FIG. 36 a-c shows the dissolution behavior of LPCVD nitride, PECVD-LFnitride (low frequency, LF) and PECVD-HF nitride (high frequency, HF) inbuffer solutions (pH 7.4 to 12) at RT and 37° C. Here, three factors(temperature, pH and film characteristics) were considered. Thedissolution rate increases with temperature, as expected. FIG. 36 d andFIG. 9 show the pH dependence, which is similar to that observed in theoxides. The kinetics suggests a linear relationship between dissolutionrate and pH according to log r=a+n [pH], where n ranges from 0.11 to0.28 for 37° C. and 0.26 to 0.31 for RT. As with the oxides, thenitrides were studied in bovine serum at 37° C. and sea water at RT; therates are ˜8 times and ˜4 times higher than those at similar pH inbuffer solution, likely due to chemical substances in the serum and seawater (FIG. 10).

Effects of stoichiometry and density were also investigated. Table 2shows that the stoichiometry of the LPCVD film is Si₃N_(3.9), while thatof the PECVD films is Si₃N_(4.3) (LF) and Si₃N_(3.3) (HF).

TABLE 2 Atomic concentration of different silicon nitrides measured byXPS. Carbon (C) and fluorine and (F) are considered surfacecontamination (%) Si N F C x (Si₃N_(x)) LPCVD Si₃N₄ 36.3 47.8 5.3 10.73.9 PECVD-LF Si₃N₄ 35.2 50.6 6.2 8.1 4.3 PECVD-HF Si₃N₄ 36.9 40.1 11.811.2 3.3

FIG. 36 e and FIG. 37 show the dependence of the dissolution rate onaverage film density. The densities are 3.1 g/cm³ for LPCVD, 3.0 g/cm³for PECVD-LF and 2.5 g/cm³ for PECVD-HF. The results suggest that LPCVDnitride exhibits the lowest dissolution rate, at least partly due to itsfavorable stoichiometry and high density. PECVD-HF nitride shows thefastest dissolution rate due to its non-stoichiometric chemistry and itslow density. The modified reactive diffusion model described previouslycan provide some utility in capturing the effects of porosity, subjectto limitations associated with its approximations. From the results ofFIG. 36 a-c, the reaction constants (k) were found to be 8.0×10⁻⁸,4.5×10⁻⁷, and 4.0×10⁻⁷ s⁻¹ for LPCVD nitride, PECVD-LF nitride andPECVD-HF nitride, respectively, in buffer solution (pH 7.4) at 37° C. bymodified reactive diffusion model where the density of closely packedamorphous nitrides was 3.16 g/cm³.

Encapsulation Strategy with Inorganic Layers

In addition to their use as gate and interlayer dielectrics, siliconoxides and nitrides can be considered as transientpassivation/encapsulation layers. These materials are well known to begood barrier materials for permeation of water vapor in conventionalelectronics.^([4,5,30,31]) Previous research^([4,31]) on encapsulationwith PECVD oxide and nitride in organic light-emitting diode (OLED)devices indicates that defects, such as pinholes, are a primary cause ofleakage of vapors or fluids. We show here that multilayer structures ofboth silicon oxides and nitrides can reduce such defects and that thesematerials can be used in transient electronics.

As shown in FIG. 19, a combination of multiple different layers, i.e.SiO₂ and Si₃N₄, improves the performance of the encapsulation. Multiplelayers with different materials can reduce water/vapor permeationthrough an underlying layer, by cooperative elimination ofdefects.^([4,31]) Atomic layer deposition (ALD) provides a complementarystrategy to reduce effects arising from defects.^([32,33]) A doublelayer of PECVD SiO₂ (or PECVD-LF Si₃N₄) and ALD SiO₂ representseffective means of encapsulation, even with thin layers (FIG. 19). Thedissolution rate of a single layer of ALD SiO₂ is 0.08 nm/day in buffersolution (0.1 M, pH 7.4) at 37° C. (FIG. 38), similar to that of PECVDSiO₂ in the same conditions.

FIG. 20 presents measured changes in resistance of a serpentine-shapedMg trace (˜300 nm), with several encapsulation approaches at varioustimes for immersion in deionized water at room temperature. Samples witha single layer of ALD SiO₂ (˜20 nm), PECVD SiO₂ or Si₃N₄ (˜1 μm) showincreases in resistance after just a few hours of immersion. Acombination of PECVD SiO₂ (˜500 nm) and Si₃N₄ (˜500 nm) extends thistime to ˜1 day. Triple layers of PECVD SiO₂ and Si₃N₄ (˜200 nm/200nm/200 nm/200 nm/100 nm/100 nm, total thickness ˜1 μm) extend to ˜10days. Combinations of PECVD SiO₂/ALD SiO₂ (˜500/20 nm) and PECVDSi₃N₄/ALD SiO₂ (˜500/20 nm) show characteristic times of ˜5 and ˜7 days,respectively. These results suggest that the ALD SiO₂ layer has muchfewer defects than PECVD SiO₂ or Si₃N₄. A single layer of ALD (˜20 nm)provides similar timescale as a single layer of SiO₂ or Si₃N₄ (˜1 μm).Although combined used of PECVD SiO₂ and ALD SiO₂ shows extendedlifetimes, a single layer of ALD SiO₂ itself is not sufficiently thickto cover uniformly the sorts of structures found in transientelectronics, with the Mg resistor (˜300 nm) as a simple example. Thesedissolution behaviors lead to two-stage kinetics in the functionaltransience of this test structure: i) encapsulation layers define thefirst time period, i.e. stable operation with negligible changes inelectrical properties, ii) the Mg defines the second, i.e. rapiddegradation in function. The optical microscope images in FIG. 21clearly reveal that the dissolution of Mg begins with leakage of waterfrom local defects, which then quickly propagate laterally. Theseresults suggest that an efficient encapsulation strategy is criticallyimportant in removing these leakage pathways, to increase the time forstable operation. Also, encapsulation with these inorganic materials canbe improved by combined use of biodegradable polymers as suggested inprevious encapsulation studies in OLED devices.^([31,34])

CONCLUSION

The results reported here provide a foundation of understanding ofhydrolysis in silicon oxides and nitrides for applications in transientelectronics, and their dependence on temperature, pH and filmproperties. An appealing aspect of these materials for theseapplications is that they are already well developed and widely used inconventional electronics. Opportunities range not only from gate andinterlayer dielectrics to passivation and encapsulation layers but alsoto window layers and antireflection coatings in photovoltaics oroptoelectronics systems.

Studies of the kinetics of hydrolysis of thin films of silicon oxidesand nitrides and the use of these materials as encapsulants werepresented for applications. Dissolution rates of various types ofsilicon oxides and nitrides were examined for their dependence on the pHand ionic concentration, temperature of the solution and the morphologyand chemistry of films. The encapsulation approaches based on multiple,different thin layers of oxides and nitrides prevent water permeationfor up to 10 days in simple transient electronic test structures.

Experimental Section

Test Structures for Silicon Oxides and Nitrides:

Thin layers of silicon oxides (SiO₂) were prepared in three differentways, all on silicon wafers (University Wafer): (1) Thermally grown(tg-oxides) (dry and wet oxidation), (2) plasma-enhanced chemical vapordeposited from precursor gases (PECVD, Trion Technology, USA) at 350°C., and (3) electron beam (E-beam) evaporated from SiO₂ pellets (99.99%,Kurt J. Lesker Company, USA). The nitrides were deposited onto similarwafers. The films were formed by low-pressure chemical vapor deposition(LPCVD) and by PECVD (Surface Technology Systems, Newport, UK) at 300°C. using low frequency (LF, 380 kHz) and high frequency (HF, 13.56 MHz).In all cases, the thickness was controlled at ˜100 nm. The teststructures for measurement by atomic force microscope (AFM) consisted ofarrays of square pads (3 μm×3 μm×100 nm), fabricated by photolithographyand reactive ion etching (RIE).

Dissolution Experiments:

Samples were placed into 50 mL of aqueous buffer solutions withdifferent pH (pH 7.4-12, Sigma-Aldrich, USA) at either room temperature(RT) or physiological temperature (37° C.). Studies also involved bovineserum (pH ˜7.4, Sigma-Aldrich, USA) at 37° C. and sea water (pH ˜7.8) atroom temperature. In all cases, the samples were removed from thesolutions, rinsed with DI water, and measured by spectroscopicellipsometry (J. A. Wooldman Co. Inc., USA) to determine thicknessand/or atomic force microscopy (AFM, Asylum Research MFP-3D, USA) todetermine both the thickness and surface morphology. After suchmeasurements, each of which lasted a few hours, the samples werereturned to the solutions. The solutions were replaced every other day.

Characterization of Film Properties:

Film density was measured using X-ray reflectometry (XRR, X'pert MRDSystem, Netherlands). X-ray photoelectron spectroscopy was performedwith a system from Axis ULTRA, UK. To avoid surface oxidation of thenitrides, the measurements were conducted shortly after oxide removal inbuffered oxide etchant (BOE, 6:1, Transene Company Inc., USA) for a fewseconds. Transmission electron microscopy (TEM, JEOL 2010F (S)TEM, USA)was used to study the porous microstructure of the PECVD and E-beamoxides.

Encapsulation Tests:

Serpentine traces of Mg (˜300 nm thick) were defined by e-beamevaporation and liftoff using a patterned layer of photoresist (AZ 2070,MicroChem, USA) on a glass substrate. Each trace was then encapsulatedwith various overcoats of PECVD SiO₂, PECVD-LF Si₃N₄, and ALD SiO₂(Savannah, Cambridge Nanotech, USA). Encapsulation layers at both endsof the trace were removed by RIE, to allow continuous measurement ofchanges in resistance while immersed in aqueous solutions.

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Example 4 Polyanhydrides for Transient Encapsulation

Several polyanhydrides were prepared from various combinations ofanhydrides, linkers and thiols, which were combined and irradiated withUV light to initiate a polymerization or curing reaction. The reagentcombinations are shown in Table 3. The polyanhydrides were screened toidentify candidates for transient encapsulation. Mixtures were testedfor UV curability, film integrity, stability toward delamination andstability for 1 day toward dissolution. Passing results are indicatedwith Os and negative results are indicated with Xs. From these results,mixture 7A was selected as the candidate with the highest potential fora transient organic encapsulant characterized by UV curability, goodfilm integrity, stability toward delamination and stability towarddissolution for at least 1 day.

TABLE 3 Combinations of anhydrides, linkers and thiols to yieldpolyanhydrides. Sta- ble Sta- for 1 ble day Film for dis- UV Inte- de-sol'n Anhydride Linker Thiol Cure grity lam. test 1A

X — — — 1B X

X — — — 2A

◯ ◯ ◯ ▴ 2B X

◯ X (Cracks) ◯ ▴ 3A

◯ ◯ X X 3B X

X — — — 4A

◯ ◯ ◯ ▴ 4B X

◯ ◯ ◯ ▴ 5A

X — — — 5B X

X — — — 7A

◯ ◯ ◯ ◯ 7B X

◯ ◯ ◯ ◯

The ratio of anhydride and hydrophobic chain compound (i.e., thiol) inmixture 7A was tuned to optimize transient encapsulation properties. Asshown in FIG. 39A, 4-pentanoic anhydride contains a degradable chain andtwo alkene end groups capable of reacting with 1,4-butane dithiol.1,3,5-triallyl-1,3,5-triazene-2,4,6(1H, 3H, 5H)-trione contains threealkene groups capable of reacting with 1,4-butane dithiol. FIG. 39Bprovides the ratios of each component and shows that degradation rateincreases as hydrophobicity decreases (hydrophilicity increases). Thisresult is consistent with water permeating a hydrophilic encapsulantmore rapidly than a hydrophobic encapsulant.

FIGS. 39C-E show additional polyanhydride encapsulant materials formedby photocuring mixtures of one or more anhydride monomers and one ormore thiol monomers. FIG. 39C shows a polyanhydride encapsulant materialincorporating a phosphodiester group within the polymeric chain. Thephosphodiester group increases susceptibility of the polymer todegradation by base and/or enzymes. FIG. 39D shows a polyanhydrideencapsulant material incorporating a silyl ether group within thepolymeric chain. The silyl ether group increases susceptibility of thepolymer material to degradation by acid. FIG. 39E shows a polyanhydrideencapsulant material incorporating an ether group within the polymericchain. The ether group increases susceptibility of the polymer materialto degradation by acid. As shown by these examples, suitable polymericencapsulants may be synthesized and/or selected to achieve a selectedprogrammable transience under a specific environment.

FIG. 40 shows a schematic of a water permeability test set-up. Amagnesium conductor is applied to a glass substrate and two extendedelectrodes are soldered to ends of the conductor to monitor resistanceas a function of time. An organic encapsulant, such as 7A, is appliedover the entire device, which is located in a petri dish. DI water isadded over the organic encapsulant.

FIG. 41 shows performance of organic encapsulants compared to materialsof other classes, such as inorganic encapsulants, as a function ofchange in conductor resistance over time. A1TX is the polyanhydridesynthesized by combining pentanoic anhydride and 1,3,5 triallyl-1,3,5triazene-2,4,6 (1H, 3H, 5H) trione with a 1:X molar concentration.(SiO₂/SiN)X3 describes a multilayer stack of triple layers of siliconoxide and silicon nitride (SiO₂/SiN/SiO₂/SiN/SiO₂/SiN). PDMS ispoly(dimethyl siloxane). BCB is bisbenzocyclobutene, a non-degradablepolymer for comparison with degradable organic and inorganicencapsulants. A1T4 had the lowest water permeation within thepolyanhydride class. Combining inorganic and organic encapsulation((SiO₂/SiN)X3+ A1T4) gave the best results (˜27 days). Multiple layershelped to cover defect of previous layers and had better performanceagainst water permeation. In this example, the step of depositing theinorganic layer occurred at 200˜350° C., which the organic layer couldnot withstand without undergoing a chemical and/or physicaltransformation. Thus, the inorganic layer was applied first, with a toporganic layer serving as a mechanical buffer layer because the organiclayer is less brittle than the inorganic layer.

In an embodiment, multilayer inorganic-organic encapsulation may includealternating organic and inorganic layers. For example, a first organiclayer may cover an electronic device. The organic layer may be conformaland/or may be an electrical insulator. A second encapsulation layer,applied on top of the first organic layer may be an inorganic layer forreducing water permeability. A third encapsulation layer, applied on topof the second encapsulation layer, may be an organic layer, e.g., forfilling pinholes or defects in the underlying inorganic layer.

In an embodiment, multilayer inorganic-organic encapsulation may includealternating organic and inorganic devices. For example, an inorganiclayer may be applied over an electronic device. The inorganic layer maybe conformal and/or may be an electrical insulator. A secondencapsulation layer, applied on top of the first inorganic layer, may bean organic layer, e.g., for filling pinholes or defects in the firstinorganic layer. A third encapsulation layer, applied on top of thesecond encapsulation layer, may be an inorganic layer, e.g., forreducing water permeability.

In alternative embodiments, multilayer inorganic-organic encapsulationstacks may include organic layers in direct contact with neighboringorganic layers and/or inorganic layers in direct contact withneighboring inorganic layers.

In an embodiment, a multilayer encapsulation stack comprises two, three,four, five, six, seven,eight, nine, ten, twelve, fifteen, twenty or morelayers.

FIGS. 42A-C show the dissolution rates of three polyanhydrides (A1T1,A1T2, A1T4) in buffer solutions with pH 5.7 (squares), pH 7.4 (circles)and pH 8 (triangles). The dissolution rates of the polyanhydrides washighest in acid and lowest in base. A1T4 has low water permeability(FIG. 41) but a slow dissolution rate due to a low concentration ofanhydride.

STATEMENTS REGARDING INCORPORATION BY REFERENCE AND VARIATIONS

All references cited throughout this application, for example patentdocuments including issued or granted patents or equivalents; patentapplication publications; and non-patent literature documents or othersource material; are hereby incorporated by reference herein in theirentireties, as though individually incorporated by reference, to theextent each reference is at least partially not inconsistent with thedisclosure in this application (for example, a reference that ispartially inconsistent is incorporated by reference except for thepartially inconsistent portion of the reference).

The following references relate generally to flexible and/or stretchablesemiconductor materials and devices. Each is hereby incorporated byreference in its entirety: U.S. patent application Ser. No. 12/778,588,filed on May 12, 2010, PCT International Application No. PCT/US05/19354,filed Jun. 2, 2005 and published under No. WO2005/122285 on Dec. 22,2005, U.S. Provisional Patent Application No. 61/313,397, filed Mar. 12,2010, U.S. patent application Ser. No. 11/851,182, filed Sep. 6, 2007and published under No. 2008/0157235 on Jul. 3, 2008, and PCTInternational Application No. PCT/US07/77759, filed Sep. 6, 2007 andpublished under No. WO2008/030960 on Mar. 13, 2008.

The following references relate generally to bioresorbable substratesand methods of making bioresorbable substrates. Each is herebyincorporated by reference in its entirety: PCT Patent ApplicationPCT/US03/19968 filed Jun. 24, 2003, PCT Patent ApplicationPCT/US04/000255 filed Jan. 7, 2004, PCT Patent ApplicationPCT/US04/11199 filed Apr. 12, 2004, PCT Patent ApplicationPCT/US05/20844 filed Jun. 13, 2005, and PCT Patent ApplicationPCT/US06/029826 filed Jul. 28, 2006.

The following references relate generally to transient electronicdevices. Each is hereby incorporated by reference in its entirety: U.S.patent application Ser. No. 13/624,096 and PCT International ApplicationNo. PCT/US2012/056538, each filed Sep. 21, 2012.

The terms and expressions which have been employed herein are used asterms of description and not of limitation, and there is no intention inthe use of such terms and expressions of excluding any equivalents ofthe features shown and described or portions thereof, but it isrecognized that various modifications are possible within the scope ofthe invention claimed. Thus, it should be understood that although thepresent invention has been specifically disclosed by preferredembodiments, exemplary embodiments and optional features, modificationand variation of the concepts herein disclosed may be resorted to bythose skilled in the art, and that such modifications and variations areconsidered to be within the scope of this invention as defined by theappended claims. The specific embodiments provided herein are examplesof useful embodiments of the present invention and it will be apparentto one skilled in the art that the present invention may be carried outusing a large number of variations of the devices, device components,and method steps set forth in the present description. As will beobvious to one of skill in the art, methods and devices useful for thepresent methods can include a large number of optional composition andprocessing elements and steps.

When a group of substituents is disclosed herein, it is understood thatall individual members of that group and all subgroups, including anyisomers, enantiomers, and diastereomers of the group members, aredisclosed separately. When a Markush group or other grouping is usedherein, all individual members of the group and all combinations andsubcombinations possible of the group are intended to be individuallyincluded in the disclosure. When a compound is described herein suchthat a particular isomer, enantiomer or diastereomer of the compound isnot specified, for example, in a formula or in a chemical name, thatdescription is intended to include each isomers and enantiomer of thecompound described individually or in any combination. Additionally,unless otherwise specified, all isotopic variants of compounds disclosedherein are intended to be encompassed by the disclosure. For example, itwill be understood that any one or more hydrogens in a moleculedisclosed can be replaced with deuterium or tritium. Isotopic variantsof a molecule are generally useful as standards in assays for themolecule and in chemical and biological research related to the moleculeor its use. Methods for making such isotopic variants are known in theart. Specific names of compounds are intended to be exemplary, as it isknown that one of ordinary skill in the art can name the same compoundsdifferently.

The following references relate generally to fabrication methods,structures and systems for making electronic devices, and are herebyincorporated by reference to the extent not inconsistent with thedisclosure in this application.

It must be noted that as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural reference unless thecontext clearly dictates otherwise. Thus, for example, reference to “acell” includes a plurality of such cells and equivalents thereof knownto those skilled in the art, and so forth. As well, the terms “a” (or“an”), “one or more” and “at least one” can be used interchangeablyherein. It is also to be noted that the terms “comprising”, “including”,and “having” can be used interchangeably. The expression “of any ofclaims XX-YY” (wherein XX and YY refer to claim numbers) is intended toprovide a multiple dependent claim in the alternative form, and in someembodiments is interchangeable with the expression “as in any one ofclaims XX-YY.”

Attorney Application Filing Publication Publication Patent Issue DocketNo. No. Date No. Date No. Date 145-03 US 11/001,689 Dec. 01, 20042006/0286488 Dec. 21, 2006 7,704,684 Apr. 27, 2010 18-04 US 11/115,954Apr. 27/2005 2005/0238967 Oct. 27, 2005 7,195,733 Mar. 27, 2007 38-04AUS 11/145,574 Jun. 02, 2005 2009/0294803 Dec. 03, 2009 7,622,367 Nov.24, 2009 38-04B US 11/145,542 Jun. 02, 2005 2006/0038182 Feb. 23, 20067,557,367 Jul. 07, 2009 43-06 US 11/421,654 Jun. 01, 2006 2007/0032089Feb. 08, 2007 7,799,699 Sep. 21, 2010 38-04C US 11/423,287 Jun. 09, 20062006/0286785 Dec. 21, 2006 7,521,292 Apr. 21, 2009 41-06 US 11/423,192Jun. 09, 2006 2009/0199960 Aug. 13, 2009 7,943,491 May 17, 2011 25-06 US11/465,317 Aug. 17, 2006 — — — — 137-05 US 11/675,659 Feb. 16, 20072008/0055581 Mar. 06, 2008 — — 90-06 US 11/782,799 Jul. 25, 20072008/0212102 Sep. 04, 2008 7,705,280 Apr. 27, 2010 134-06 US 11/851,182Sep. 06, 2007 2008/0157235 Jul. 03, 2008 8,217,381 Jul. 10, 2012 151-06US 11/585,788 Sep. 20, 2007 2008/0108171 May 08, 2008 7,932,123 Apr. 26,2011 216-06 US 11/981,380 Oct. 31, 2007 2010/0283069 Nov. 11, 20107,972,875 Jul. 05, 2011 116-07 US 12/372,605 Feb. 17, 2009 — — — —213-07 US 12/398,811 Mar. 05, 2009 2010/0002402 Jan. 07, 2010 8,552,299Oct. 08, 2013 38-04D US 12/405,475 Mar. 17, 2009 2010/0059863 Mar. 11,2010 8,198,621 Jun. 12, 2012 170-07 US 12/418,071 Apr. 03, 20092010/0052112 Mar. 04, 2010 8,470,701 Jun. 25, 2013 38-04A1 US 12/564,566Sep. 22, 2009 2010/0072577 Mar. 25, 2010 7,982,296 Jul. 19, 2011 71-07US 12/669,287 Jan. 15, 2010 2011/0187798 Aug. 04, 2011 — — 60-09 US12/778,588 May 12, 2010 2010/0317132 Dec. 16, 2010 — — 43-06A US12/844,492 Jul. 27, 2010 2010/0289124 Nov. 18, 2010 8,039,847 Oct. 18,2011 15-10 US 12/892,001 Sep. 28, 2010 2011/0230747 Sep. 22, 20118,666,471 Mar. 4, 2014 15-10AUS 14/140,299 Dec. 24, 2013 — — — — 19-10US 12/916,934 Nov. 01, 2010 2012/0105528 May 03, 2012 8,562,095 Oct. 22,2013 3-10 US 12/947,120 Nov. 16, 2010 2011/0170225 Jul. 14, 2011 — —118-08 US 12/996,924 Dec. 08, 2010 2011/0147715 Jun. 23, 2011 — — 126-09US 12/968,637 Dec. 15, 2010 2012/0157804 Jun. 21, 2012 — — 50-10 US13/046,191 Mar. 11, 2011 2012/0165759 Jun. 28, 2012 — — 151-06A US13/071,027 Mar. 24, 2011 2011/0171813 Jul. 14, 2011 — — 137-05A US13/095,502 Apr. 27, 2011 — — — — 216-06B US 13/100,774 May 04, 20112011/0266561 Nov. 03, 2011 — — 38-04A2 US 13/113,504 May 23, 20112011/0220890 Sep. 15, 2011 8,440,546 May 14, 2013 136-08 US 13/120,486Aug. 04, 2011 2011/0277813 Nov. 17, 2011 — — 151-06B US 13/228,041 Sep.08, 2011 2011/0316120 Dec. 29, 2011 — — 43-06B US 13/270,954 Oct. 11,2011 2012/0083099 Apr. 05, 2012 8,394,706 Mar.12, 2013 3-11 US13/349,336 Jan. 12, 2012 2012/0261551 Oct. 18, 2012 — — 38-04E US13/441,618 Apr. 06, 2012 2013/0100618 Apr. 25, 2013 — — 134-06B US13/441,598 Apr. 06, 2012 2012/0327608 Dec. 27, 2012 — — 28-11 US13/472,165 May 15, 2012 2012/0320581 Dec. 20, 2012 — — 7-11 US13/486,726 Jun. 01, 2012 2013/0072775 Mar. 21, 2013 — — 29-11 US13/492,636 Jun. 08, 2012 2013/0041235 Feb. 14, 2013 — — 84-11 US13/549,291 Jul. 13, 2012 2013/0036928 Feb. 14, 2013 — — 25-06A US13/596,343 Aug. 28, 2012 2012/0321785 Dec. 20, 2012 8,367,035 Feb. 05,2013 150-11 US 13/624,096 Sep. 21, 2012 2013/0140649 Jun. 06, 2013 — —38-04A3 US 13/801,868 Mar. 13, 2013 2013/0320503 Dec. 05, 2013 8,664,699Mar. 04, 2014 38-04A4 US 14/155,010 Jan. 14, 2014 — — — — 125-12 US13/835,284 Mar. 15, 2013 — — — — 30-13 US 13/853,770 Mar. 29, 2013 — — ——

Unless defined otherwise, all technical and scientific terms used hereinhave the same meanings as commonly understood by one of ordinary skillin the art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, the preferred methodsand materials are now described. Nothing herein is to be construed as anadmission that the invention is not entitled to antedate such disclosureby virtue of prior invention.

Whenever a range is given in the specification, for example, a range ofintegers, a temperature range, a time range, a composition range, orconcentration range, all intermediate ranges and subranges, as well asall individual values included in the ranges given are intended to beincluded in the disclosure. As used herein, ranges specifically includethe values provided as endpoint values of the range. As used herein,ranges specifically include all the integer values of the range. Forexample, a range of 1 to 100 specifically includes the end point valuesof 1 and 100. It will be understood that any subranges or individualvalues in a range or subrange that are included in the descriptionherein can be excluded from the claims herein.

As used herein, “comprising” is synonymous and can be usedinterchangeably with “including,” “containing,” or “characterized by,”and is inclusive or open-ended and does not exclude additional,unrecited elements or method steps. As used herein, “consisting of”excludes any element, step, or ingredient not specified in the claimelement. As used herein, “consisting essentially of” does not excludematerials or steps that do not materially affect the basic and novelcharacteristics of the claim. In each instance herein any of the terms“comprising”, “consisting essentially of” and “consisting of” can bereplaced with either of the other two terms. The inventionillustratively described herein suitably can be practiced in the absenceof any element or elements, limitation or limitations which is notspecifically disclosed herein.

One of ordinary skill in the art will appreciate that startingmaterials, biological materials, reagents, synthetic methods,purification methods, analytical methods, assay methods, and biologicalmethods other than those specifically exemplified can be employed in thepractice of the invention without resort to undue experimentation. Allart-known functional equivalents, of any such materials and methods areintended to be included in this invention. The terms and expressionswhich have been employed are used as terms of description and not oflimitation, and there is no intention in the use of such terms andexpressions of excluding any equivalents of the features shown anddescribed or portions thereof, but it is recognized that variousmodifications are possible within the scope of the invention claimed.Thus, it should be understood that although the invention has beenspecifically disclosed by preferred embodiments and optional features,modification and variation of the concepts herein disclosed can beresorted to by those skilled in the art, and that such modifications andvariations are considered to be within the scope of this invention asdefined by the appended claims.

1. A transient electronic device comprising: a substrate; one or moreactive or passive electronic device components supported by saidsubstrate; wherein said active or passive electronic device componentsindependently comprise a selectively transformable material; and anencapsulant layer at least partially encapsulating said one or moreactive or passive electronic device components; wherein said substrate,said encapsulant layer or both independently comprise a selectivelyremovable inorganic material responsive to an external or internalstimulus; wherein at least partial removal of said substrate, saidencapsulant layer or both in response to said external or internalstimulus initiates at least partial transformation of said one or moreactive or passive electronic device components providing a programmabletransformation of the transient electronic device in response to saidexternal or internal stimulus at a pre-selected time or at apre-selected rate, wherein said programmable transformation provides achange in function of the transient electronic device from a firstcondition to a second condition.
 2. The device of claim 1, wherein saidone or more active or passive electronic device components comprise oneor more inorganic semiconductor components, one or more metallicconductor components or one or more inorganic semiconductor componentsand one or more metallic conductor components.
 3. The device of claim 1,wherein said substrate, said encapsulant layer or both independentlycomprise an entirely inorganic structure or a composite inorganic andorganic structure.
 4. The device of claim 3, wherein said entirelyinorganic structure comprises one or more of SiO₂, spin-on-glass, Mg, Mgalloys, Fe, W, Zn, Mo, Si, SiGe, Si₃N₄ and MgO.
 5. The device of claim3, wherein said composite inorganic and organic structure comprises aninorganic layer having a first surface adjacent said active or passiveelectronic device components and a second surface adjacent an organiclayer or an organic layer having a first surface adjacent said active orpassive electronic device components and a second surface adjacent saidinorganic layer.
 6. (canceled)
 7. The device of claim 3, wherein saidinorganic layer comprises one or more of SiO₂, spin-on-glass, Mg, Mgalloys, Fe, W, Zn, Mo, Si, SiGe, Si₃N₄ and MgO and said organic layercomprises one or more of a polyanhydride and poly(di methyl siloxane)(PDMS).
 8. The device of claim 1, wherein said device is an entirelyinorganic device, wherein said active or passive electronic devicecomponents, said substrate and said encapsulant layer each areindependently entirely composed of one or more inorganic materials. 9.The device of claim 1, wherein said substrate, said encapsulant layer orboth independently have a preselected transience profile in response tosaid external or internal stimulus.
 10. The device of claim 1, whereinsaid selectively removable inorganic material of said substrate, saidencapsulant layer or both independently comprises a metal, a metaloxide, a ceramic or a combination of these, a crystalline material, anamorphous material or a combination thereof, a single crystallinematerial, polycrystalline material or doped crystalline material, aglass, a thin film, a coating, a foil or any combination of these, or ananostructured layer or a microstructured layer. 11-15. (canceled) 16.The device of claim 1, wherein said selectively removable inorganicmaterial of said substrate, said encapsulant layer or both independentlycomprises Mg, W, Mo, Fe, Zn, or an alloy thereof, SiO₂ MgO, N₄Si₃, SiC,a spin-on-glass, a solution processable glass, a biocompatible material,a bioinert material or a combination of biocompatible and bioinertmaterials. 17-19. (canceled)
 20. The device of claim 1, wherein saidsubstrate, said encapsulant layer or both independently comprise amultilayer structure comprising one or more thin films, coatings, orfoils comprising said selectively removable inorganic material.
 21. Thedevice of claim 20, wherein said substrate, said encapsulant layer orboth independently comprises a composite inorganic and organic structurehaving a multilayer geometry.
 22. The device of claim 20, wherein saidmultilayer structure further comprises one or more electricallyinsulating layers, barrier layers or any combinations thereof; whereinsaid one or more electrically insulating layers or barrier layers isprovided in physical contact, electrical contact or both with said oneor more thin films, coatings, or foils; wherein said one or moreelectrically insulating layers or barrier layers comprises an exteriorlayer of said multilayer structure or wherein said one or moreelectrically insulating layers or barrier layers comprises an interiorlayer of said multilayer structure in physical contact or electricalcontact with said one or more active or passive electronic devicecomponents; or wherein said one or more electrically insulating layersor barrier layers comprises a polymer, an insulating ceramic, a glass,SiO₂, spin-on glass, MgO or any combination of these. 23-25. (canceled)26. The device of claim 20, wherein said multilayer structure comprisesa metal foil or thin metal film having a first side in physical contactwith a first electronically insulating layer or barrier layer; whereinsaid first electronically insulating layer or barrier layer is anexterior layer of said multilayer structure or wherein said firstelectronically insulating layer or barrier layer is an interior layer ofsaid multilayer structure in physical contact or electrical contact withsaid active or passive electronic device components; wherein said firstelectronically insulating layer or barrier layer comprises a polymerlayer or coating, a metal oxide layer or coating, a glass layer orcoating or any combination of these; wherein said multilayer structurecomprises said metal foil or thin metal film having a second side coatedin contact with a second electronically insulating layer or barrierlayer; or wherein said metal foil or thin metal film is provided betweensaid first electronically insulating layer or barrier layer and saidsecond electronically insulating layer or barrier layer. 27-29.(canceled)
 30. The device of claim 1, wherein said at least partialremoval of said substrate, said encapsulant layer or both exposes saidone or more active or passive electronic device components to saidexternal or internal stimulus, thereby initiating said at least partialtransformation of said one or more active or passive electronic devicecomponents.
 31. The device of claim 1, wherein said at least partialremoval of said substrate, said encapsulant layer or both in response tosaid internal or external stimulus occurs via a phase change,dissolution, hydrolysis, bioresorption, etching, corrosion, aphotochemical reaction, an electrochemical reaction or any combinationof these processes.
 32. The device of claim 1, wherein said substrate,said encapsulant layer or both independently have a preselectedtransience profile characterized by a removal of 0.01% to 100% of saidsubstrate or said encapsulant layer over a time interval selected fromthe range of 1 ms to 5 years or a decrease in average thickness of saidsubstrate or said encapsulant layer at a rate selected over the range of0.01 nm/day to 100 microns s⁻¹.
 33. (canceled)
 34. The device of claim1, wherein said substrate, said encapsulant layer or both independentlyhave a porosity selected from the range of 0.01% to 99.9%, an extent ofcrystallinity selected from the range of 0.01% to 100%, or a densityselected from the range of 0.01% to 100% compared to bulk prior to saidat least partial removal of said substrate, said encapsulant layer orboth in response to said external or internal stimulus.
 35. (canceled)36. (canceled)
 37. The device of claim 1, wherein a time for a thicknessof said selectively removable inorganic material to reach zero isprovided by the expression:${t_{c} = {\frac{4\rho_{m}{M\left( {H_{2}O} \right)}}{{kw}_{0}{M(m)}}\frac{\sqrt{\frac{{kh}_{0}^{2}}{D}}}{\tanh \sqrt{\frac{{kh}_{0}^{2}}{D}}}}};$where t_(c) is the critical time, ρ_(m) is the mass density of thematerial, M(H₂O) is the molar mass of water, M(m) is the molar mass ofthe material, h₀ is the initial thickness of the material, D is thediffusivity of water, k is the reaction constant for the dissolutionreaction, and w_(o) is the initial concentration of water; wherein k hasa value selected from the range of 1×10⁵ s⁻¹ to 1×10⁻¹⁰ s⁻¹.
 38. Thedevice of claim 1, wherein said substrate, said encapsulant layer orboth are substantially impermeable to water, limit a net leakage currentto the surroundings to 0.1 μA/cm² or less, or undergo an increase involume equal to or less than 10% upon exposure to an aqueous ornonaqueous solvent prior to said at least partial removal of saidsubstrate, said encapsulant layer or both in response to said externalor internal stimulus.
 39. (canceled)
 40. (canceled)
 41. The device ofclaim 20, wherein said thin film, coating, or foil has an averagethickness over or underneath of said one or more active or passiveelectronic device components less than or equal to 1000 μm prior to saidat least partial removal of said substrate, said encapsulant layer orboth in response to said external or internal stimulus.
 42. The deviceof claim 1, wherein said substrate, said encapsulant layer or bothindependently have a thickness selected from the range of 0.1 μm to 1000μm, an average modulus selected over the range of 0.5 KPa to 10 TPa, anet flexural rigidity less than or equal to 1×10⁻⁴ Nm, or a net bendingstiffness less than or equal to 1×10⁸ GPa μm⁴ prior to said at leastpartial removal of said substrate, said encapsulant layer or both inresponse to said external or internal stimulus. 43-45. (canceled) 46.The device of claim 1, wherein said substrate, said encapsulant layer orboth are at least partially optically transparent in the visible orinfrared regions of the electromagnetic spectrum.
 47. The device ofclaim 1, wherein said substrate, said encapsulant layer or both aregenerated via physical vapor deposition, chemical vapor deposition,sputtering, atomic layer deposition, electrochemical deposition, spincasting, electrohydrodynamic jet printing, screen printing or anycombination of these.
 48. The device of claim 1, wherein said substrate,said encapsulant layer or both cover or support a percentage of anexterior area or an interior area of said one or more active or passiveelectronic device components selected from the range of 1% to 100% orwherein said substrate, said encapsulant layer or both cover or support10% or more of an exterior area or an interior area of said one or moreactive or passive electronic device components.
 49. (canceled)
 50. Thedevice of claim 2, wherein said one or more inorganic semiconductorcomponents comprise a polycrystalline semiconductor material, singlecrystalline semiconductor material or a doped polycrystalline or singlecrystalline semiconductor material, Si, Ga, GaAs, ZnO or any combinationof these.
 51. (canceled)
 52. The device of claim 2, wherein said one ormore metallic conductor components comprise Mg, W, Mo, Fe, Zn or analloy thereof.
 53. The device of claim 2, wherein said one or moreinorganic semiconductor components, one or more metallic conductorcomponents or both comprise a component of an electronic device selectedfrom the group consisting of a transistor, a diode, an amplifier, amultiplexer, a light emitting diode, a laser, a photodiode, anintegrated circuit, a sensor, a temperature sensor, an electrochemicalcell, a thermistor, a heater, a resistive heater, an antenna, a battery,an energy storage system, an actuator, a nanoelectromechanical system ora microelectromechanical system, and an actuator and arrays thereof. 54.The device of claim 1, wherein said device is a communication system, aphotonic device, a sensor, an optoelectronic device, a biomedicaldevice, a temperature sensor, a photodetector, a photovoltaic device, astrain gauge, an imaging system, a wireless transmitter, anelectrochemical cell, an antenna, a battery, an energy storage system,an actuator, a nanoelectromechanical system or a microelectromechanicalsystem.
 55. A method of using a transient electronic device, said methodcomprising the steps of: providing the transient electronic devicecomprising: a substrate; one or more active or passive electronic devicecomponents supported by said substrate; wherein said active or passiveelectronic device components independently comprise a selectivelytransformable material; and an encapsulant layer at least partiallyencapsulating said one or more active or passive electronic devicecomponents; wherein said substrate, said encapsulant layer or bothindependently comprise a selectively removable inorganic materialresponsive to an external or internal stimulus; wherein at least partialremoval of said substrate, said encapsulant layer or both in response tosaid external or internal stimulus initiates at least partialtransformation of said one or more active or passive electronic devicecomponents providing a programmable transformation of the transientelectronic device in response to said external or internal stimulus at apre-selected time or at a pre-selected rate, wherein said programmabletransformation provides a change in function of the transient electronicdevice from a first condition to a second condition; and exposing saidtransient electronic device to said external or internal stimulusresulting in said at least partial removal of said substrate orencapsulant layer to expose said one or more active or passiveelectronic device components to said external or internal stimulus,thereby providing said programmable transformation of the transientelectronic device. 56-61. (canceled)
 62. A method of making a transientelectronic device, said method comprising the steps of: providing asubstrate; providing on said substrate one or more active or passiveelectronic device components; wherein said active or passive electronicdevice components independently comprise a selectively transformablematerial; and at least partially encapsulating said one or more activeor passive electronic device components with an encapsulant layer;wherein said substrate, said encapsulant layer or both independentlycomprise a selectively removable inorganic material responsive to anexternal or internal stimulus; wherein at least partial removal of saidsubstrate, said encapsulant layer or both in response to said externalor internal stimulus initiates at least partial transformation of saidone or more active or passive electronic device components providing aprogrammable transformation of the transient electronic device inresponse to said external or internal stimulus at a pre-selected time orat a pre-selected rate, wherein said programmable transformationprovides a change in function of the transient electronic device from afirst condition to a second condition.